Enable explicit include and lib paths for FreeType, FreeImage and gl2ps

Configure on Linux only allows to specify a single directory to FreeImage, FreeType and gl2ps (options –with-freetype, –with-freeimage, and –with-gl2ps). OCC makes pre-defined assumptions on locations inside those directories.

This is not flexible and is not aligned with other options (e.g. –with-tbb-include and –with-tbb-library) which allow to specify explicit locations.

When the former three products are built by a user then the locations may be different from pre-defined (this is the case for CAD Exchanger for instance). We have to work-around use of single variables by creating symlinks which has its own downsides.

The request is to enable support of dual options consistent with other products.