Moved branch-argument for ls_tree to options-hash (i.e. :branch => 'mybranch') and adapted code and specs accordingly. Reworked stringify to use a String instead of a StringIO object. Added missing 'require 'stringio'', as it is used in Tree.data.
Cosmetic update, changed 'java_import' to 'import'.
Merge branch 'master' of ssh://github.com/repotag/rjgit