convert: Work around p4 instability (issue2465)

The p4 command-line client sometimes fails upon doing "p4 describe"
when trying to produce a patch. (I'm guessing it's a bug in p4.)
However, "hg convert" doesn't even make use of the patch, and it can
be elided by adding "-s" to the p4 command line here.

hgext/convert/p4.py

@@ -105,10 +105,9 b' class p4_source(converter_source):'
         ui.status(_('collecting p4 changelists\n'))
         lastid = None
         for change in self.p4changes:
-            cmd = "p4 -G describe %s" % change
+            cmd = "p4 -G describe -s %s" % change
             stdout = util.popen(cmd, mode='rb')
             d = marshal.load(stdout)
-
             desc = self.recode(d["desc"])
             shortdesc = desc.split("\n", 1)[0]
             t = '%s %s' % (d["change"], repr(shortdesc)[1:-1])