Fix what appears to be a cut-and-paste bug in NSDictionary.FilePermissions.
Add omitted Else block in NSDictionary.FileCreationDate.
Fix code in NSDictionary.AllKeys; tweak some other related code for style.
Revise NSDictionary and NSMutableDictionary; update other code that uses these classes.
Merge pull request #73 from declaresub/master

Revise NSDictionary and NSMutableDictionary