Make 'svnfsfs load-index' more convenient to use in case the revision footer is corrupted or missing. Also, as long as the footer is valid, make sure the new index actually covers all revision contents.
* subversion/libsvn_fs_fs/load-index.c (get_max_covered): New utility function. (svn_fs_fs__load_index): In case of a footer parser error, truncate the rev file where the coverage of new index data ends. Otherwise, require the coverage to be the same as the old index coverage.
* subversion/tests/libsvn_fs_fs/fs-fs-private-test.c (load_index): Update test to pass the stricter internal checks.