These invocations occur before we can actually automatically install git via
bottle, and as such their output isn't relevant.

Open the incomplete download in append mode instead of write mode.
Opening in write mode truncates the existing file, so curl keeps
restarting downloads instead of resuming the incomplete downloads.

Apparently `cellar :any_skip_relocation` doesn't actually mean we
can skip relocation, at least for text files.

We were deleting pyc files *after* replace_locations_with_placeholders
and recording changed_files, meaning that some of the recorded files
were to be deleted. The correct order is the opposite.

A sample failed session: https://bot.brew.sh/job/Homebrew%20Core/10080/version=el_capitan/testReport/junit/brew-test-bot/el_capitan/bottle_buku/.

Replace relocate_text_files with three methods that clarify intent:
replace_locations_with_placeholders, replace_placeholders_with_locations
and replace_text_in_files, the first two calling the third.

`brew bottle` replaces instances of the Homebrew prefix, cellar, and
repository with placeholders in all text files. Cache these files in
INSTALL_RECEIPT.json so that we don't have to check every single text
file for placeholders on install.

Stable URLs should not use unstable versions.

New name is HOMEBREW_CASK_TAP_CASK_REGEX

- Stop supporting archaic "user-repo/token" syntax
- Move regex for parsing tapped Cask token to tap_constants