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.
GL.GLSL: Hide GL.GLSL and GL.GLSLUtils when not supported
Configure [GL.GLSL]: Survive without GLSL.
The configure script now no longer aborts if the dependencies
for the GL.GLSL module aren't met.
Also adds a feature line to the main configuration report.
Fixes multiple build failures in Pikefarm.
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.