README: Add debian package install commands

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
waffle: replace GL with OpenGL

This replaced cases of GL with OpenGL in documents, comments
and printed strings.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: Brian Paul <brianp@vmware.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
glx: Remove unused variable

src/waffle/glx/glx_context.c:72:25: warning: unused variable 'dpy' [-Wunused-variable]
    struct glx_display *dpy = glx_display(config->wcore.display);

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
core: Fix missing space in error message

before: "for OpenGL >= 3.2,WAFFLE_CONTEXT_PROFILE must be"
after:  "for OpenGL >= 3.2, WAFFLE_CONTEXT_PROFILE must be"

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>