fix-ftgl-includes

fix-ftgl-includes

Fix detection of FTGL in configure.in

Also modify installed headers to search for FTGL headers in
the right directory.  This is not needed to build opencascade,
but may help people including those headers.
And last, fix usage of FTGL, FTFace is an internal structure
of FTGL and is no more exported.

Submitted upstream: http://www.opencascade.org/org/forum/thread_20128/

Gbp-Pq: Topic submitted
Gbp-Pq: Name fix-ftgl-includes.patch