Fixed Issue #2219: Canonicalize values in svn:keywords.

   * subversion/libsvn_wc/props.c
     (canonicalize_keywords): New function  to 
     canonicalize the input based on the canonical 
     values defined for svn:keywords.
     (svn_wc_prop_set2): Changed function to call 
     canonicalize_keywords().

   * subversion/tests/clients/cmdline/prop_tests.py
     (prop_value_conversions): Modified function to  
     reflect output changes now caused by canonicalization.

   * subversion/tests/clients/cmdline/trans_tests.py
     (canonicalize_keywords_prop): New function for  
     testing canonicalization of svn:keywords.
     (canonicalized_and_keywords_expanded): New function 
     for testing canonicalization of svn:keywords
     and expansion of keywords inside the file.