Email mangling in archives breaks links

The mailing list archives web interface obfuscates email addresses by
replacing @ and . with (at) and (dot). That breaks links to other
messages in the archives, which after mangling, look like this:

http://www.postgresql.org/message-id/CA+TgmobguVO+qHnHvxBA2TFkDhw67Y=4Bp405FVABEc_EtO4VQ(at)mail(dot)gmail(dot)com

Attached is a patch to fix that. It changes the simple regexp used to
replace @ and . to check that there is no "/message-id/" string before
the email address (which isn't actually an email address in those links).

- Heikki