SBConstrain fix
spelling
SBRoundedPathS
SBTabbarItem
shorten drawing code in SBSavePanel

(which is apparently not currently used in any live code, oops)
shorten SBBookmarksView drawing code
NSBitmapImageRep-SBAdditions
NSScrollView-SBAdditions (unused?)
NSURL-SBAdditions
NSMenu-SBAdditions
improve organization a bit

move Additions from Classes to a new directory, and SBUtil.h/m to Sources where it should have been