fix(exrc): lua exrc files know their location
Problem:
'exrc' files are inherently bound to their location / workspace and
therefore require to "know" their location on the filesystem. However,
currently using `debug.getinfo(1, 'S')` returns `"<nvim>"`.
Solution:
Include the filepath as chunkname in `loadstring()` and `nlua_exec()`.
f7c939fa7a
