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

mercurial/hgweb/request.py

@@ -298,6 +298,9 b' def parserequestfromenv(env, reponame=No'
     if 'CONTENT_LENGTH' in env and 'HTTP_CONTENT_LENGTH' not in env:
         headers['Content-Length'] = env['CONTENT_LENGTH']
 
+    if 'CONTENT_TYPE' in env and 'HTTP_CONTENT_TYPE' not in env:
+        headers['Content-Type'] = env['CONTENT_TYPE']
+
     bodyfh = env['wsgi.input']
     if 'Content-Length' in headers:
         bodyfh = util.cappedreader(bodyfh, int(headers['Content-Length']))