Merge remote-tracking branch 'origin/8.1' into peter/travis
GL.GLSL: Merge GL and GL_GLSL modules.
These two modules are closely related and link to the same libraries.
No Pike-level API changes.
Configure [GL.GLSL]: Fix build problems on some platforms.
Make sure that the <GL/gl.h> header file can be found.
GL.GLSL: Check for the correct libGL to use
This is heavily cargo-culted from post_modules/GL, but should now let
Pike compile on platforms with no libGL.
GL.GLSL: Fix Makefile.in, unbreak testsuite.
Add GL.GLSL and GL.GLSLUtil.
This was a project by Per Hedbor that he intended to prepare for
inclusion in Pike and shared as a separate repository on the pike-git
server, albeit yet in the form of an external module. We have now
performed the integration into Pike as a post_module.