hgweb: cast bytearray to bytes

PEP-3333 seems to indicate that bytes is the only allowed type that can
be used to express the output of a WSGI application. And some WSGI
environments seem to enforce this (mod_wsgi does).

This commit universally casts bytearray instances to bytes to appease
the WSGI specification.

I found this because wireprotov2 is emitting bytearray instances. I'd
like to keep things that way because the way it builds a data
structure, bytearray is more efficient. I'd rather keep the low-level
code efficient (and using bytearray) and cast at the edges than impose
a performance penalty on code that may run outside WSGI contexts.

mercurial/hgweb/request.py

@@ -540,6 +540,12 b' class wsgiresponse(object):'
             yield self._bodybytes
         elif self._bodygen:
             for chunk in self._bodygen:
+                # PEP-3333 says that output must be bytes. And some WSGI
+                # implementations enforce this. We cast bytes-like types here
+                # for convenience.
+                if isinstance(chunk, bytearray):
+                    chunk = bytes(chunk)
+
                 yield chunk
         elif self._bodywillwrite:
             self._bodywritefn = write