convert: move localname state to function scope

convert: use return value in parse_view() instead of manipulating state

changegroup: simplify logic around enabling changegroup 03 There was multiple spot that took care of adding '03' as supported changegroup version for different condition. We gather them all in one location for simplicity. The 'supportedincomingversions' function is now doing nothing, but I kept it around because it looks like a great hooking point for extension. (Note that we should probably just get changegroup3 out of experimental now, But that would be a patch with a much wider scope).

changegroup: pass 'repo' to allsupportedversions In the next changesets, we will introduce more logic directly related to the repository to decide what version have to be supported. So we now directly pass the repo object instead of just ui.

changegroup: simplify 'allsupportedversions' logic Discarding '03' to add it back is a bit strange. Instead we only discard it when needed.

py3: replace os.altsep with pycompat.altsep All the occurences of os.altsep are replaced with pycompat.altsep which returns bytes.

py3: have a bytes version of sys.platform sys.platform returns unicodes on Python 3. This patch adds up pycompat.sysplatform which returns bytes.

py3: have a bytes version of os.altsep os.altsep returns unicodes on Python 3. We need a bytes version hence added pycompat.altsep.