[Pydev-code] Some debugger fixes

[Aleks T. <a...@to...>]

Hi,
I've just checked in some fixes to the debugger. It is better, 
but still not perfect. My main fix was to PySourceLocator, it now 
avoids calling doOpenEditor. This required refactoring the 
"External Files" hack in PydevPlugin.

The only remaining bug that I know of is the stack display. It 
seems to get out of sync. I've tried to track it down. My code 
returns the right number of stack items, but for some reason 
Eclipse does not refresh its view properly. Looks like they did a 
lot of debugger changes that changed the threads/control flow, 
and I'll have to dig in deeper to figure out where the refresh 
code is getting confused. I'll be on vacation until Aug 16th, so 
there will not be any new updates until then.

Aleks