configure: Really read gfx-course.conf

The path lacked a '/'.
gc_log: Add funcs gc_logd_loc, gc_logd_func

I need debug messages that optionally contain the source location and
function name.
gc_array: Add little array helpers

Define functions below:
    gc_float_array_alloc
    gc_float_array_append
    gc_uint32_array_alloc
    gc_uint32_array_append

This will when passing arrays around as callback data.
gc_util: Define gc_gl_drain_error()
gc_drawable: Replace the Georgia Tech PLY library wth rply

rply has a sane API.