Added workaround for PyQt/uuid crashes.

Fixes #775.
Fixed pollution of GafferUI namespace with IECore module.

Also added the Gaffer import that must be made before _GafferUI can import (due to order of boost::python::class_ registrations) so that it is no longer for programmers to do that themselves.
Added DirNameParameterValueWidget.

This is a specialised version of the PathParameterValueWidget which filters the file browser so that only directories are displayed.

Fixes #774.
Merge pull request #779 from johnhaddon/dirNameParameterFiltering

Added DirNameParameterValueWidget.
Merge pull request #778 from johnhaddon/uuid

UUID/PyQt crash workaround
Fixed the ImageView swatches so that they draw correctly when no alpha is present.