Ensure that the p2l index file format in FSFS is independent of the
machine's endianess.

We handle FNV-1 checksums as integers and shall only use a definitive
byte order in the digest and on disk.  I.e. we must no longer do a
conversion of the result in the checksum function itself.

The on-disk part is handled by the integer stream already (always little
endian) but we used a big endian input before.  Hence, the on-disk
representation changes.  For the digest part, we convert to / from big
endian when writing to the digest / reading from it.

FSX is not affected ATM as it does not use index checksums, yet.

* subversion/libsvn_fs_fs/fs_fs.c
  (write_revision_zero): Update the checksum parts of the rev 0 template.

* subversion/libsvn_subr/fnv1a.c
  (finalize_fnv1a_32x4, 
   svn__fnv1a_32): The checksum value is no longer platform dependent.

* subversion/libsvn_subr/checksum.c
  (svn_checksum,
   svn_checksum_final): Make sure the digest has a definitive, platform
                        independent byte order.

* subversion/libsvn_fs_fs/transaction.c
  (fnv1a_checksum_finalize): Convert from byte ordering used in the
                             digest back to host order.

* subversion/libsvn_fs_fs/verify.c
  (expected_streamed_checksum): Same.

Patch by: philip

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1573371 13f79535-47bb-0310-9956-ffa450edef68