Set default global tag in case none is found from environment
Add GlobalTag as command-line argument
Avoid name conflict
Merge pull request #340 from dabelknap/ntuple_globaltag

Ntuple globaltag
Added try/except block to catch user systems setting change crashes
Added except statement to handle user systems setting change crashes
Import errno in Dispatcher.py so it knows how to do the previously committed fix
Merge pull request #343 from nwoods/crash_fix

Fix crazy client-side system settings change crashes