Port `cherry-pick`, `pull-request` tests to cukes

Port a bunch more tests to cukes

[gh] Merge in master (v1.12.2) and fix all tests

Fix `git --noop clone` with private repos

Fixes #593

expect(x).to_not returns false when the test passes, so using history.all? only
checks the first element of the list. Since expect raises anyway, we
don't need to bother anyway.

As suggested by @mislav, the the previous assertion only checked against
"git clone" without parameters.

Conflicts:
	Gemfile.lock
	features/browse.feature

Also get rid of deprecation warnings for `should` and `failure_message_for_should`

Still won't work for Enterprise gists, but this makes it work for pull
request & commit URLs.

Fixes #584

When a fix for #466 landed, it was necessary to escape slashes in branch
names with `;` because they weren't supported as a path component in
compare URLs. Now slashes are supported, but GitHub stopped supporting
semicolons as means of escaping.

Fixes #588

Instead of stderr, show this help on stdout because we suppose that the
user intended to retrieve help intentionally.