hgweb: be sure to drain request data even in early error conditions
Thanks to Mads Kiilerich with noticing this. The hg client can only read data
after all the sent data has been read, so we have to read all the request data
even if we're not going to do anything with it (in error conditions). This
is not easy to fix in the client, because we're using Python's httplib, which
is strictly stateful. Abstracted the draining into a separate method.
#header#
<!-- Changelog -->
<id>{urlbase}{url}</id>
<link rel="self" href="{urlbase}{url}atom-log"/>
<link rel="alternate" href="{urlbase}{url}"/>
<title>#repo|escape# Changelog</title>
#latestentry%feedupdated#
#entries%changelogentry#
</feed>