([NSCharacterSet +initialize]): New method.
([NSCharacterSet _bitmapForSet:number:]): Return set from cache if
available, otherwise find bitmap file and add to cache. All callers
changed.
git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@1667 72102866-910b-0410-8b05-ffd578937521