tests/test-diff-issue2761.t

hgweb: also set Content-Type header

Our HTTP/WSGI server may convert the Content-Type HTTP request
header to the CONTENT_TYPE WSGI environment key and not set
HTTP_CONTENT_TYPE. Other WSGI server implementations
do this, so I think the behavior is acceptable.

So assuming this HTTP request header could get "lost" by the WSGI
server, let's restore it on the request object like we do for
Content-Length.

FWIW, the WSGI server may also *invent* a Content-Type value. The
default behavior of Python's RFC 822 message class returns a default
media type if Content-Type isn't defined. This is kind of annoying.
But RFC 7231 section 3.1.1.5 does say the recipient may assume a media
type of application/octet-stream. Python's defaults are for
text/plain (given we're using an RFC 822 parser). But whatever.

Differential Revision: https://phab.mercurial-scm.org/D2849

Test issue2761

  $ hg init

  $ touch to-be-deleted
  $ hg add
  adding to-be-deleted
  $ hg ci -m first
  $ echo a > to-be-deleted
  $ hg ci -m second
  $ rm to-be-deleted
  $ hg diff -r 0

Same issue, different code path

  $ hg up -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ touch does-not-exist-in-1
  $ hg add
  adding does-not-exist-in-1
  $ hg ci -m third
  $ rm does-not-exist-in-1
  $ hg diff -r 1