Fixed VectorDataWidget bool delegate for PySide.

PySide seems to have a few deficiencies in this area compared to PyQt - see comments for details.
Improved VectorDataWidget numeric editing.

We now use a GafferUI.NumericWidget for editing rather than a QWhateverItWas. This provides a more consistent experience with the rest of Gaffer and fixes some graphical problems.

Fixes #637.
Simplified OpDialogue exception reporting.

We now output the full stacktrace only at debug level, to help users focus on the simpler message that hopefully the exception contains.

Fixes #806.
Merge pull request #809 from johnhaddon/vectorDataWidgetNumericDelegate

VectorDataWidget fixes
Merge pull request #810 from johnhaddon/opDialogueTraceback

Simplified OpDialogue exception reporting.
Fixed "Open Recent..." crash bug in PySide builds.

Fixes #548.
Merge pull request #811 from johnhaddon/openRecentCrashFix

Fixed "Open Recent..." crash bug in PySide builds.
Added workaround for Coverity build failure.