remotefilelog: tell runbgcommand to not block on child process startup

These two invocations will always find a binary because they're
re-running hg. As a result, we can skip waiting for the subprocess to
start running and save a little bit of wall-time.

Differential Revision: https://phab.mercurial-scm.org/D6539

hgext/remotefilelog/repack.py

@@ -43,7 +43,8 b' def backgroundrepack(repo, incremental=T'
     if packsonly:
         cmd.append('--packsonly')
     repo.ui.warn(msg)
-    procutil.runbgcommand(cmd, encoding.environ)
+    # We know this command will find a binary, so don't block on it starting.
+    procutil.runbgcommand(cmd, encoding.environ, ensurestart=False)
 
 def fullrepack(repo, options=None):
     """If ``packsonly`` is True, stores creating only loose objects are skipped.

hgext/remotefilelog/shallowrepo.py

@@ -190,7 +190,9 b' def wraprepo(repo):'
                 cmd.append('--repack')
             if revs:
                 cmd += ['-r', revs]
-            procutil.runbgcommand(cmd, encoding.environ)
+            # We know this command will find a binary, so don't block
+            # on it starting.
+            procutil.runbgcommand(cmd, encoding.environ, ensurestart=False)
 
         def prefetch(self, revs, base=None, pats=None, opts=None):
             """Prefetches all the necessary file revisions for the given revs