Fixes Homebrew/homebrew#21417.

Closes Homebrew/homebrew#21390.

Closes Homebrew/homebrew#21385.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

eql? should not depend on the hash value as hash values of uneql objects
can collide, but eql values may only collide for objects that are
actually eql.

Further, python dependencies are uniquely identified by the combination
of the name and imports attributes, so there is no reason to involved
the expensive binary computation for simple equality checks.

Fixes Homebrew/homebrew#20840.

This was worded in a confusing way, and made an assumption about future
OS X versions that we don't know to be true.

Also, it's probably wrong to state that the CLT location is dependent on
the OS X version; surely there will be a newer CLT for 10.8 that gets
installed in the same location as on 10.9. But we don't know any better
yet.

I'm tired of not remembering if start_with?/end_with? are portable, so
just add them both if they're not defined.

It is supposed to accept a variable number of prefixes, and also to
check if they are convertible to strings. This matches behavior
documented in RubySpec.

This check was only occurring in one branch of the conditional.
As a result, if you ran `brew upgrade` with no args and there were no packages to upgrade,
the nonsensical message

"==> Upgrading 0 outdated package, with result:"

would be printed.

Closes Homebrew/homebrew#21316.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

This is needed for local bottle installation and also possible when
detecting bottle versions from URLs.

Needs a less hacky fix but at least this will stop failing tests.