transplant: use peer of source repository as "remote" for "repo.pull()"

Before this patch, transplant with "--merge" option fails with
traceback unexpectedly, if it causes pull from the source repository
on the local host.

"discovery.findcommonincoming()" invokes "capable()" method on the
object given from "localrepository.pull()", but it is
"localrepository" object in this case and doesn't have such method.

This patch uses peer object of source repository as "remote" argument
for "localrepository.pull()" invocation like other invocations of it
in transplant.py.

hgext/transplant.py

@@ -154,7 +154,7 b' class transplanter(object):'
                     # transplants before them fail.
                     domerge = True
                     if not hasnode(repo, node):
-                        repo.pull(source, heads=[node])
+                        repo.pull(source.peer(), heads=[node])
 
                 skipmerge = False
                 if parents[1] != revlog.nullid:

tests/test-transplant.t

@@ -430,6 +430,20 b' test transplant into empty repository'
   adding manifests
   adding file changes
   added 4 changesets with 4 changes to 4 files
+
+test "--merge" causing pull from source repository on local host
+
+  $ hg --config extensions.mq= -q strip 2
+  $ hg transplant -s ../t --merge tip
+  searching for changes
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 2 changesets with 2 changes to 2 files
+  applying a53251cdf717
+  4:a53251cdf717 merged at 4831f4dc831a
+
   $ cd ..