Add support to the 'svnmerge' tool for unique labels embedded in the merge tracking property names. Provide a new command line flag -L to specify a specific label to use.
Add support to the 'svnmerge' tool for unique labels embedded in the merge
tracking property names. Provide a new command line flag -L to specify a
specific label to use.

This adds support for two situations where 'svnmerge' didn't work due to
properties with the same name conflicting:

  1. When there are multiple 'head' dirs from which merges are being tracked
  2. When the 'head' tree is itself tracking merges from yet another 'head'
     (e.g., when two trees are tracking merges from each other)

* contrib/client-side/svnmerge:
  Added support for unique property labels using the -L flag

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion