Fixed issue where the same file could be open twice.

If you have a file A open and then open a solution where file A is in
the user preferences, then file A will be opened twice.

This fix makes sure that a file is not already open when loading the
user preferences for a solution.
Do not hide debug command bar if we are exiting the MonoDevelop.
Merge pull request #44 from Unity-Technologies/unity-4.5-staging

Cherry picked unity-trunk fixes for Unity 4.5