Fix for: Sorting when external sorting is enabled is broken

Provides fix for the following condition:
When external sorting is enabled, attempting to sort via multiple
columns is futile because as soon as you click the column, all of the
sorting turns off.  The problem is related NG-Grid improperly handling
an unexpected DOM event.
Fix for: Sorting when external sorting is enabled is broken

Provides fix for the following condition:
When external sorting is enabled, attempting to sort via multiple
columns is futile because as soon as you click the column, all of the
sorting turns off.  The problem is related NG-Grid improperly handling
an unexpected DOM event.  Behavior is unmodified if no externalsorting
is false.
Merge branch '2.0.8' of https://github.com/velocityware/ng-grid into velocityware-2.0.8
Merge branch '2.0.8' of https://github.com/angular-ui/ng-grid into 2.0.8
bumping version number to match the fork

-- added shane and myself to the team