Extended the FS file checksum test.  Verify committed data and SHA1
checksums as well where we only used to check for MD5 in transactions.

* subversion/tests/libsvn_fs/fs-test.c
  (verify_file_checksum): New utility function, code mainly taken from ...
  (verify_checksum): ... this test.  Invoke the new utility for MD5
                     and SHA1 as well as before and after the commit.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1633973 13f79535-47bb-0310-9956-ffa450edef68