set ident-width of BitAttributedLabel to 4 spaces

seems this is the used one, so set it in the xcodeproject
fix mem leak
fix warning 'multiple methods length found'

* method accepts either NSStrings and NSAttributedString: assert on that
* explicitly cast to NSAttributedString to get rid of ambiguity warning
fix mem-leak analyzer warning

Although the analyzer is wrong here (highlighFramesetter property is synthesized), it doesn't hurt
to use the instance variables.
fix analyzer warning

it's somewhat more clear to release and set to nil,
then store a new reference directly in the ivar.
Merge pull request #43 from diederich/fix/analyzerWarnings

Fix analyzer warnings