Get rid of compiler warning about unused function `write_string':
Get rid of compiler warning about unused function `write_string':

(DELTIFYING): New #define, set to 0.
(write_string_baton, write_string): Guard definitions with DELTIFYING.
(svn_fs__rep_deltify): Guard body with DELTIFYING.

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