Two changes to ease CI:
1) If pysvn is missing, the tests for svn_helper don't run and pollute the
output
2) svn_helper no longer depends on being located at trunk/scripts/
Patch by: Augie Fackler
Review by: Todd Larsen
Review Issue: 802
Reviewed URL: http://codereviews.googleopensourceprograms.com/802