mac/xcode: update expected Clang on 10.13

docs: Clarify availability of analytics

audit: fix subversion remote check logic.

This commit tweaks the language in Analytics.md to make it clear
that summaries of install/error data are publicly available,
while only Homebrew maintainers can access the full analytics
(as specified above in the document).

audit: Add some heuristics to https upgrade checks

Stop flagging invalid URLs as valid and vice-versa.

Fixes #3118.

Java: deprecate ENV.java_cache in favour of setting it by default.

Added tests for utils/git

gpg: tweaks

Offline cask search and listing all available casks 

search_remote_tap spec: fix test offline

Even though we stub the JSON response, the method being tested always
returns [] immediately if HOMEBREW_NO_GITHUB_API is set.

pour_bottle?: Pour local bottles without sha256

github: limit PR search to Homebrew

Don't fail to migrate repo because of empty dir

I just ran into an issue where a colleague's Homebrew couldn't update.
It seems to have been because it failed once just after the new repo
directory was created. Since there was nothing in this directory, there
really isn't any reason for us to fail here, so to avoid this problem in
the future, try to `rmdir` the directory before failing because it already
exists.

missing_formula: update for Pillow's brew demise.

Not sure whether this is the way you want to handle this problem but
it's really darn irritating so here's a PR that handles it one way.

Fixes: https://github.com/Homebrew/brew/pull/3086#issuecomment-324519156

Pouring a local bottle for a formula without a bottle sha256
in the formula for that OS would unexpectedly install from
source instead.

Don't ignore f.pour_bottle? and compatible_cellar? when pouring
a local bottle. --force-bottle may be used to pour a local
bottle that is incompatible, as it is for remote bottles.

Added tests for utils/svn

Added tests for utils/analytics

Ref: https://github.com/Homebrew/homebrew-core/pull/17341
Ref: https://github.com/Homebrew/homebrew-core/pull/17357