add check for matlab compiler

[tsnouidui]

Original reporter: mwetter

If users use the
Lcc-win32 C 2.4.1 compiler
which is distributed with MATLAB, and compile the matlab interface, then bcvtb.dll cannot be loaded by matlab.

The error function seems to be

loadlibrary('bcvtb.dll', @bcvtb)

Mex file entry point is missing. Please check the (case-sensitive)
spelling of mexFunction (for C MEX-files), or the (case-insensitive)
spelling of MEXFUNCTION (for FORTRAN MEX-files).
??? Error using ==> loadlibrary at 441

(See also google groups.)

Add a check that gives a meaningful error message, and add instructions to the documentation.