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