OpenGL:  Don't name VS inputs as 'geom' inputs.

Geometry shaders come after vertex shaders, not before.
OpenGL: Don't call glGetAttribLocation on outputs

Previously we were using glGetAttribLocation on all inputs/outputs and
then just discarding if it was returned -1.  However, we have a boolean
value of 'input' in gl_parser_attrib, so there's no need to be doing
this and discarding potentially useful error handling information.