Use the PR repo

Fixes #192 
This fails with

```
sebastien@sbesson1:snoopycrimecop ((8947a27...)) $ python scc/main.py merge master --info -I manics/snoopycrimecop:test
2014-11-25 11:10:05,853 [   scc.merge] INFO  Listing Pull Request(s) based on master
2014-11-25 11:10:05,854 [   scc.merge] INFO  Including Pull Request(s) opened by any public member of the organization
2014-11-25 11:10:05,854 [   scc.merge] INFO  Including manics/snoopycrimecop Branches(s)/Pull Request(s) test
2014-11-25 11:10:05,854 [   scc.merge] INFO  Including Pull Request(s) labelled as include
2014-11-25 11:10:05,854 [   scc.merge] INFO  Excluding Pull Request(s) labelled as exclude or breaking
Traceback (most recent call last):
  File "scc/main.py", line 76, in entry_point
    (UpdateSubmodules.NAME, UpdateSubmodules),
  File "/usr/local/lib/python2.7/site-packages/yaclifw/framework.py", line 197, in main
    ns.func(ns)
  File "/Users/sebastien/code/ome/snoopycrimecop/scc/git.py", line 2865, in __call__
    updated = self.merge(args, self.main_repo)
  File "/Users/sebastien/code/ome/snoopycrimecop/scc/git.py", line 2895, in merge
    set_commit_status=args.set_commit_status)
  File "/Users/sebastien/code/ome/snoopycrimecop/scc/git.py", line 1589, in rmerge
    merge_msg += self.origin.merge_info()
  File "/Users/sebastien/code/ome/snoopycrimecop/scc/git.py", line 791, in merge_info
    for repo, branch in self.candidate_branches[remote]:
TypeError: 'Repository' object is not iterable
```

I suppose either using iteritems
```
for remote, repo_branches in self.origin.candidate_branches.iteritems():
```

or 

```
    for repo_branch in self.candidate_branches[remote]:
        branch=repo_branch[1]
```

should fix this.