Provide a fallback luaL_setfuncs() for Lua 5.1

The LGI bindings are failing at runtime because of the above missing
function. Added it to compat.c: implementation borrowed from Lua wiki.
Merge pull request #49 from ntd/pr2

Raise an exception if GTK+ initialization fails
When running 'make check', always pick local lgi

This should help when developing lgi and also having older stable lgi
installed in default Lua path.

https://github.com/pavouk/lgi/issues/47
Supporting cairo.Status.to_string API

Giving access to cairo_status_to_string() can be quite handy for error
reporting.

https://github.com/pavouk/lgi/pull/44
Revert "Provide a fallback luaL_setfuncs() for Lua 5.1"

This reverts commit 2d9725e1543e1118714806bce7fa0b77b779affd.
Check http://github.com/pavouk/lgi/pull/51 for details.
Merge branch 'upstream' into devel

Conflicts:
	tests/cairo.lua