rmerge() now returns an updated status boolean

Resurrects the functionality preventing the push if no submodule pointer has been bumped

```
sbesson:openmicroscopy sebastien$ git checkout origin/develop && git submodule update 
M	components/bioformats
M	docs/sphinx
HEAD is now at 8df63e8... Merge pull request #692 from will-moore/getLabel_bug
Submodule path 'components/bioformats': checked out '55b680e70ff0f987b980bcd814dca0e751be696a'
Submodule path 'docs/sphinx': checked out 'fba35366ecbe0b9d8b68d5b05b03def22611b3fb'
sbesson:openmicroscopy sebastien$ python ~/code/scc/scc.py update-submodules develop --push submodules/feb_7
2013-02-07 13:38:01,929 [scc.update-s] INFO  Updating submodules
2013-02-07 13:38:32,287 [scc.update-s] INFO  Repository: openmicroscopy/openmicroscopy
2013-02-07 13:38:32,287 [scc.update-s] INFO  Already up-to-date.
2013-02-07 13:38:32,287 [scc.update-s] INFO  
2013-02-07 13:38:32,287 [scc.update-s] INFO  Repository: openmicroscopy/bioformats
2013-02-07 13:38:32,287 [scc.update-s] INFO  Updating 55b680e..948c5e4
2013-02-07 13:38:32,287 [scc.update-s] INFO  
2013-02-07 13:38:32,287 [scc.update-s] INFO  Repository: ome/scripts
2013-02-07 13:38:32,287 [scc.update-s] INFO  Already up-to-date.
2013-02-07 13:38:32,287 [scc.update-s] INFO  
2013-02-07 13:38:32,287 [scc.update-s] INFO  Repository: openmicroscopy/ome-documentation
2013-02-07 13:38:32,288 [scc.update-s] INFO  Updating fba3536..647af9e
2013-02-07 13:38:32,288 [scc.update-s] INFO  
2013-02-07 13:38:41,076 [scc.update-s] INFO  Merged branch pushed to https://github.com/sbesson/openmicroscopy/tree/submodules/feb_7
sbesson:openmicroscopy sebastien$ python ~/code/scc/scc.py update-submodules develop --push submodules/feb_7
2013-02-07 13:39:04,280 [scc.update-s] INFO  Updating submodules
2013-02-07 13:39:36,197 [scc.update-s] INFO  Repository: openmicroscopy/openmicroscopy
2013-02-07 13:39:36,197 [scc.update-s] INFO  Already up-to-date.
2013-02-07 13:39:36,197 [scc.update-s] INFO  
2013-02-07 13:39:36,197 [scc.update-s] INFO  Repository: openmicroscopy/bioformats
2013-02-07 13:39:36,197 [scc.update-s] INFO  Already up-to-date.
2013-02-07 13:39:36,197 [scc.update-s] INFO  
2013-02-07 13:39:36,197 [scc.update-s] INFO  Repository: ome/scripts
2013-02-07 13:39:36,197 [scc.update-s] INFO  Already up-to-date.
2013-02-07 13:39:36,198 [scc.update-s] INFO  
2013-02-07 13:39:36,198 [scc.update-s] INFO  Repository: openmicroscopy/ome-documentation
2013-02-07 13:39:36,198 [scc.update-s] INFO  Already up-to-date.
2013-02-07 13:39:36,198 [scc.update-s] INFO  
sbesson:openmicroscopy sebastien$ 
```