Review comment and patch by kkolinko -
PR 54596: Review comments and patch by kkolinko -
followup to r1647684:

- Remove unused cp argument from skip_prefix()
- Ensure sp hidden return value from skip_prefix()
  is always initialized
- Check valid use of skip_prefix() in relative
  path situation
- Simplify dots skipping code


git-svn-id: https://svn.apache.org/repos/asf/tomcat/jk/trunk@1647746 13f79535-47bb-0310-9956-ffa450edef68