The repository push email can be very expensive to generate, especially
with syntax-highlighted diffs. Instead of generating the email for each
recipient, generate one email object and reset the Message-Id and To
headers for each recipient. (Cloning would also be expensive in the case
of large emails, although probably not as bad as generating from
scratch.)
Rails' "url_helpers" method creates an anonymous Module (which a bunch
of methods) on every call. By caching the output of this method in a
dedicated method we can shave off about 10 seconds of loading time for
an issue with around 200 comments.
