Added various enhancements to the coveragediff utility:
1. coveragediff is now an ant task that is run after the test*withcoverage targets. It can be disabled with -Dtest.diff.disabled=
2. coveragediff now calls svn internally. By default it looks for svn in your path. You can specify where svn is manually by using the -Dtest.diff.svnpath property. You can also specify what files are diffed by using the -Dtest.diff.srcpath property.
3. the testcustom* targets are removed and the test* should now be used. If no no -Dtest.* properties are set, it runs the default set of tests just like before. 
4. coveragediff now generates an html report to build/diff/reports/. 
5. coveragediff now calculates coverage for modified lines overall and by file. It also lists overall number of lines modified and deleted.
6. coveragediff can function without coverage data. It will issue an warning and just generate the report w/o any coverage info. Users can use the coveragediff ant target just to generate a graphical diff.

Fix for issue 1125