[debugger-soft] Make copy of .mdb file to temp directory and open the temp copy. Update .mdb file in temp directory when original .mdb file changes. Fixes issues with not being able to update the .mdb file while the debugger is attached because MonoDevelop has it open. Case 589492
Merge pull request #45 from Unity-Technologies/unity-staging-mdb-file-locked

[debugger-soft] Open copy of .mdb and reload it on changes.