Created a new file 'common.jam' to keep rules not specific to a toolset.
* new/targets.jam: Use 'common' instead of 'utility'.
* test/project_test3.py: Test that 'clean' works.
* test/svn_tree.py: Sync with upstream revision 2944. Fix a bug
which caused empty directory to be treated as file.
[SVN r14886]
Vladimir Prus