sync with -stable

Handle exceptions in do_hgweb: Send "Internal Server Error", log traceback

various doc fixes - update can no longer be used to merge - short summary start with lowercase - add merge to short help list - fix tests

catch socket.error fix issue394

fix handling of multiple Content-type headers This can happen if an error happens while sending application/mercurial-0.1 content. The error page will be sent resulting (for at least lighttpd) in the following headers: Content-type: application/mercurial-0.1 Content-type: text/html which result in req.proto = 'application/mercurial-0.1, text/html' fix issue344

add [diff] section to hgrc documentation

inst.reason isn't alway in the form (errno, strerror) urllib2.urlopen("foobar://foo") is an example where inst.reason is a string fix issue383