Stylistic tweak, follow-up to r28172, and output fix in case an error occurs.
Stylistic tweak, follow-up to r28172, and output fix in case an error
occurs.

* subversion/svn/mergeinfo-cmd.c
  (svn_cl__mergeinfo): Check for NULL explicitly, rather than using
   the "not" operator when not in a boolean context.  Update comment
   to account for r28172.  Improve output when an error is encountered.

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