[CMake] FindMatlab.cmake suggestion

[Crni Gorac]

Could you please add a possibility to specify Matlab root installation
directory, through an environment variable, to FindMatlab.cmake
module?  For example, for non-Windows platforms, following line could
be added after line 50 of FindMatlab.cmake (and, of course, alike line
would be needed below, say after line 58 of the same file, for 64-bit
case):
    $ENV{MATLAB_DIR}/bin/glnx86/
Many other modules have alike possibility (it should be probably made
some kind of standard between modules), and the hard-coded list of
possible paths is simply too narrow).

Thanks.