Fail correctly if file passed to svn_diff_file_output_merge2() is larger 
than APR_SIZE_MAX. Otherwise we just truncate file length to apr_size_t on 
32-bit platform.

* subversion/libsvn_diff/diff_file.c
  (map_or_read_file): Change output argument type to apr_size_t instead of 
   apr_off_t. Fail if file length is larger than APR_SIZE_MAX.
  (svn_diff_file_output_merge2): Change SIZE variable type to apr_size_t.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1513122 13f79535-47bb-0310-9956-ffa450edef68