Also update command specifications to match descriptions.

Noted that this is intended for the revision of this formula instead of
rebuild of a bottle.

This would have eliminated the need for Homebrew/homebrew-core#9000, for
instance.

Given how common it is for formulae to hard-code `etc` and `var`, check
for those paths (`/usr/local/etc` and `/usr/local/var`) when determing
relocatability.

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.

Not quite a mass replacement as I've used OS X and Mac OS X where
describing specific older versions and added compatibility methods
for things in the DSL.

Now that the default from the installer, our CI and soon all users
is `/usr/local/Homebrew` it's a lot easier to check if there's
references to it (as we cannot look for `/usr/local` as it's a too
commonly hardcoded path).

Avoids issues when using `—keep-old`

Previously this was the wrong way around causing it to not be accepting
enough on e.g. a bump from :any to :any_no_relocation.

Consistent naming is good.

- Make the code more similar between `bottle` and `bottle --merge`.
- Also output the mismatched values when using `--merge`.

If fields have changed: tell the user what they were before and are
afterwards.

Also, flag those that we never want to be in a manpage.

This reverts commit 5e9bb877.

This reverts commit ec143749.

It should refuse to change existing ones but it should allow them to be
the same and silently ignore.

Ensure that the JSON file contains all the bottle checksums when using
`--keep-old`. This avoids having to use the formula DSL when merging and
relies on existing integrity checks.

This change does nothing differently if `--keep-old` is not passed.

`any?` is not the opposite of `empty?`. Besides the case that
`[false, nil].any?` will return false, `any?`(O(n)) has much worse
performance than `empty?`(O(1)).