warn on possibly conflicting opengl headers

[rurban]

a) warn if the opengl header parser finds more than one "set" of opengl headers which might lead to nci runtime conflicts.

b) support --with-opengl-include and --with-opengl-libs for disambiguation

per irc discussion with japhb and particle only warn, not fail.  http://irclog.perlgeek.de/parrot/2009-01-28#i_870777

[rurban]

r37202 clarified and changed the tricky cygwin logic:

Now we have a new limitation and DISPLAY is ignored.

• if /usr/include/GL is found then freeglut is tried,
• else w32api native GLUT is tried.
• you must uninstall freeglut and its devel packages to use native GLUT

This ticket should be used to detangle the headers from the libs. It should be possible to use native w32api GLUT with installed freeglut.

[rurban]

While working to sanify opengl on cygwin (which is currently the only platform whuich provides two possible library sets to choose) I created the attached test.

The loadlib initialization needs also to reflect the library set, so we have to take care of:

1. libs
2. matching headers
3. matching so/dll's

[rurban]

fails for a failing cygwin config "freeglut ( ÿý): failed to open display ':0.0'"