Fix typo in gles2 dlsym setup

If you happened to do both GLES2 and GLES1 in a process, it meant that
you'd try to look up v1 procs in the v2 API, and lose.  Caught by
piglit oes_fixed_point-attribute-arrays.
Test for using GLES1/2 without GLX installed.
Fix using epoxy on systems with only EGL and GLES1 or GLES2.

Fixes #19
Add a COPYING file describing the two licenses for the project code.

Fixes #20
Fix compiler warnings in the tests.

I didn't have CWARNFLAGS in the Makefile.am, so lots of things that
would generate warnings had crept in.
Enable compiler warnings in the tests.
Fix a missing \n on printing out failure to dlsym().