Changes

CMake: USE_PREBUILT_MESA_PACKAGE should only be available on Linux.

cmake/patchcmake.c: make sure it builds fine using GCC/G++ 5.x (#1391).

Updated our Mesa package (#1391).

Slight update to our QtWebKit readme file (#1391).

Updated our QtWebKit package (#1391).

Updated our CellML API package (#1391).

Updated our SBML API package (#1391).

Updated our SED-ML API package (#1391).

Temporarily disable BioSignalML-related plugins (#1391).

Updated our libigt2 package (#1391).

Updated our LibXDiff and OAuth packages (#1391).

Updated our OpenSSL package (#1391).

Updated our SUNDIALS and zlib packages (#1391).

Updated our QScintilla and Qwt packages (#1391).

Updated our Zinc package (#1391).

Updated our LLVM+Clang package (#1391).

Linux: rebuild BioSignalML libraries for GCC 5.5 (#1391).

QtWebKit package: make sure that our generated CMake files are properly
patched (#1391).

Linux: rebuild BioSignalML libraries for GCC 5.4 (#1391)

Updated our QtWebKit package (#1391).

Some minor cleaning up (#1391) [ci skip].

Zinc package: slight update to our tests until we formally upgrade to
Zinc 3.1.2 (#1391) [ci skip].

Travis CI: check whether there is an Ubuntu 16.04 LTS machine that we
could use (#1391).
Indeed, we now build everything on Ubuntu 16.04 LTS (Xenial), so to rely
on Ubuntu 14.04 LTS (Trusty) is not really an option anymore (it breaks
things; see https://travis-ci.org/opencor/opencor/jobs/263037249).

Updated our SBML and SED-ML API packages (#1391).
Indeed, our SBML API package didn’t have support for bzip2, which we 
need (for our tests, if anything). Now, because our SED-ML API package 
depends on our SBML one, we also updated it just to be on the safe side.

Travis CI: well, no Ubuntu 16.04 LTS available, so reverting to Ubuntu
14.04 LTS and see what we can do with it (#1391).
See https://travis-ci.org/opencor/opencor/jobs/263072654, although we 
asked for the xenial distribution, Travis CI doesn’t know about it and 
therefore went for its current default distribution, which is trusty.

Travis CI: see whether defining _GLIBCXX_USE_CXX11_ABI=0 makes any
difference (#1391).

Travis CI: see whether defining _GLIBCXX_USE_CXX11_ABI=0 makes any
difference (#1391).

Travis CI: see whether defining _GLIBCXX_USE_CXX11_ABI=1 makes any
difference (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Reverted part of commit abacefc (oops!) (#1391) [ci skip].

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Some minor cleaning up.

Plugin tests: make sure that their external dependencies are set in the
same way as for their corresponding plugins (#1391).
Who know, that might explain why things don’t work on Travis CI?!

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Trying to remove some RPath information on Linux (#1391).
I get the feeling that it might not be needed…

Trying to remove some RPath information on Linux (#1391).

Trying to remove some RPath information on Linux (#1391).

Ok, removing some RPath information on Linux wasn't a good idea! (#1391)

Some minor cleaning up [ci skip].

Travis CI: trying not to use GCC/G++ 5.x (#1391).
That really ought not to work!

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying not to use GCC/G++ 5.x (#1391).

Travis CI: trying not to use GCC/G++ 5.x (#1391).

Travis CI: trying not to use GCC/G++ 5.x (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Some minor cleaning up.

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Travis CI: trying to understand that GCC/G++ issue on Ubuntu (#1391).

Some minor cleaning up [ci skip].

Travis CI: temporarily (hopefully) disable building and running our
tests on Linux (#1391).
Indeed, to build our tests on Linux keeps failing. It might due to a 
discrepancy between Ubuntu 14.04 LTS (which is used on Travis CI) and 
Ubuntu 16.04 LTS, which we now use for building OpenCOR.

Travis CI: temporarily (hopefully) disable building and running our
tests on Linux (#1391).
Indeed, to build our tests on Linux keeps failing. It might due to a 
discrepancy between Ubuntu 14.04 LTS (which is used on Travis CI) and 
Ubuntu 16.04 LTS, which we now use for building OpenCOR.