Testsuite: add workaround for crash of MATLAB R2014a with TeX option

The TeX option crashes MATLAB R2014a run with "-nodisplay" option
(as is done from the testsuite). We disable the TeX option in that case.

Since we can’t directly test whether "-nodisplay" has been passed, we test for
the "TOP_TEST_DIR" environment variable, which is set by the testsuite.

Note that it was not tested whether the crash happens with more recent MATLAB
versions, so when OLD_MATLAB_VERSION is increased, one should make a test
before removing this workaround.