infinitepush: use bundleoperation.source instead of hacking on tr

Previous patches added a soutce attribute to bundle2.bundleoperation class which
stores the command which leads to current bundleoperation. Let's use that to
decide whether a processing a `hg unbundle` or not instead of hacking on
transaction.

Differential Revision: https://phab.mercurial-scm.org/D2997

hgext/infinitepush/__init__.py

@@ -927,9 +927,7 b' def storetobundlestore(orig, repo, op, u'
 def processparts(orig, repo, op, unbundler):
 
     # make sure we don't wrap processparts in case of `hg unbundle`
-    tr = repo.currenttransaction()
-    if tr:
-        if tr.names[0].startswith('unbundle'):
+    if op.source == 'unbundle':
             return orig(repo, op, unbundler)
 
     # this server routes each push to bundle store