Changes

Bug 1237 - Clarify IOUtil.getResource(..) for better efficiency, i.e.
allow caller to skip relative futile lookup
IOUtil.getResource(..) and IOUtil.ClassResources, needs more clarity.
ClassLoader shall be passed explicitly next to the optional relative
context Class instance.
This allows better efficiency, i.e. caller can pass ClassLoader but skip
a possible relative lookup, if not existing.

Bug 1237: Minor Cleanup: AssetURLContext and IOUtil.getResource(..)
DEBUG Messages

Bug 1243 - Fix IOUtil.cleanPathString(..) special case ; Allow IOUtil
and Uri to handle relative path
Fix IOUtil.cleanPathString(..) special case:
 Special case '/a/./../b' -> '/b'
 requires to resolve './' before '../'.
Allow IOUtil and Uri to handle relative path:
- IOUtil.getParentOf(..)
- IOUtil.cleanPathString(..)
 Handle cases:
  'a/./../b' -> 'b'
  '.././b' -> '../b'
- Uri: Handle null scheme