httppeer: always add x-hg* headers to Vary header...
httppeer: always add x-hg* headers to Vary header
Before, we manually updated the Vary header value for each
header contributing to it.
All X-Hg* headers are reserved for the Mercurial protocol and
could have caching implications. So it makes sense to always add
these headers to Vary.
A test revealed that X-HgArgs-Post wasn't being added to Vary.
This is only sent on POST requests. POST requests generally
aren't cacheable. However, it is possible if the server sends
the appropriate headers. Mercurial shouldn't be sending those
headers. But let's not take any chances.
Differential Revision:
https://phab.mercurial-scm.org/D3240
