Bug 10895 - Exception on solution update

Fixed an issue when submodules are out of date when issuing a repository update.
[Version Control] Git Update

Fix API break.
Modified OnUpdate to use type flags rather than additional parameter.
[Version Control] Update Command - Fixup for Submodules

Now, in case we have dirty submodules, we warn the user that he might lose changes.
We give him the option to abort, only update unchanged or discard.
Merge pull request #326 from mono/submoduleUpdate

Bug 10895 - Exception on solution update