bisect: expand help text to explain REV argument and --noupdate

keyword: thorough hgweb testing - test hgweb while keyword extension is _enabled_ - check expansion with hgweb.file - besides log and diff, also check annotate for not expanding

hgweb: raise ErrorResponses to communicate protocol errors

make streamclone.stream_out() a generator

hgweb: generate error message only if nothing is passed

strip trailing whitespace, replace tabs by spaces

hgweb: fix WSGI iterators handling in CGI adapter (issue1254)

merge with crew-stable