changegroup: use a copy of hookargs when invoking the changegroup hook addchangegroup creates a runhook function that is used to invoke the changegroup and incoming hooks, but at the time the function is called, the contents of hookargs associated with the transaction may have been modified externally. For instance, bundle2 code affects it with obsolescence markers and bookmarks info. It also creates problems when a single transaction is used with multiple changegroups added (as per an upcoming change), whereby the contents of hookargs are that of after adding a latter changegroup when invoking the hook for the first changegroup.

tests: pull common http server setup out of individual tests There are currently two different tests using roughly the same code to create temporary scripts acting as HTTP servers. As there is going to be at least one more in an upcoming change, factor those out in a standalone dumbhttp.py script.

util: move md5 back next to sha1 and allow to call it without an argument This effectively backs out changeset 908c5906091b. The API change is done so that both util.sha1 and util.md5 can be called the same way. The function is moved in order to use it for md5 checksumming for an upcoming bundle2 feature.

test-bundle2-exchange: do not drop HG_NODE from the hook output HG_NODE is precisely something we would like to test.