Fixed some compiler warnings.

* subversion/libsvn_diff/binary_diff.c
  (write_literal): Change the type of a local variable to avoid
   a 64-to-32-bit conversion warning on 64-bit platforms.
* subversion/libsvn_subr/cache-membuffer.c
  (svn_membuffer_get_segment_info): Likewise.
* subversion/libsvn_fs_base/bdb/strings-table.c
  (svn_fs_bdb__string_read): Add a cast to avoid a 64-to-32-bit
   conversion warning on 64-bit platforms.
* subversion/libsvn_fs_fs/rev_file.c
  (set_read_only): Initialize the status because it may have
   been used uninitialized.
* subversion/svn/merge-cmd.c
  (unspecified_revision): Remove unused global variable.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1607572 13f79535-47bb-0310-9956-ffa450edef68