tests: test a variety of cache invariants We've historically had a problem maintaining the expected invariants on our caches, especially when introducing new caches. This tests documents the invariants and exercises them across most of our existing cache files.

repoview: ignore unwritable hidden cache The atomictemp.close() file attempts to do a rename, which can fail. Moving the close inside the exception handler fixes it. This doesn't fit well with the with: pattern, as it's the finalizer that's failing.

tags: silence hgtagsfnodes reading failures tryread() doesn't handle "is a directory" errors and presumably others. We might not want to globally swallow such tryread errors, so we replace with our own try/except handling. An upcoming test will use directories as a portable stand-in for various bizarre circumstances that cache read/write code should be robust to.

tags: silence cache parsing errors Follow our standard STFU cache-handling pattern

i18n-pt_BR: synchronized with 18c1b107898e

ubuntu-xenial-ppa: add makefile rule