Fix "svn diff foo > bar" output.
Fix "svn diff foo > bar" output.

* diff.c (svn_cl__print_file_diff): Print diff headers using APR file
I/O to prevent output interleaving badly.

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