Fall back to "tl" if "fil" is absent.

For JB-MR1, there was a hack that used "tl" where
we really meant "fil" because ICU didn't have localizations
for "fil". This has now been fixed, and we now support 3 letter
language codes for AAPT so we can use "fil" where required.

For the benefit of apps that need to target older platforms,
we fall back to "tl" if the app has assets for "tl" and the
resource locale is "fil".

See bugs 7291355, 7207176 and 8049507 for more context.

Change-Id: I1ac8502525f99b40f9091d5efd2df33518d47a41