Fixes styling in MessageSets when prettyPrint is turned on.
=============== Diff against Tools-mt.1043 ===============
Item was changed:
----- Method: MessageSet>>aboutToStyle: (in category 'code pane') -----
"This is a notification that aPluggableShoutMorphOrView is about to re-style its text.
Set the classOrMetaClass in aPluggableShoutMorphOrView, so that identifiers
will be resolved correctly.
Answer true to allow styling to proceed, or false to veto the styling"