Fixed issues with finding wrong ids after bad commits

Unfortunately, the behaviour needed of lfs_dir_fetchwith is as subtle as
it is important. When fetching from a block corrupted by power-loss,
lfs_dir_fetch must be able to rewind any state it picks up to before the
corruption. This is not limited to the directory state, but includes
find results and other side-effects.

This gets a bit complicated when trying to generalize littlefs's
fetchwith mechanics. Being able to scan a directory block during a fetch
greatly impacts the runtime of littlefs operations, but if the state is
generic how do we know what to rollback to?

The fix here is to leave the management of rolling back state to the
fetchwith match functions, and transparently pass a CRC tag to indicate
the temporary state can be saved.

tests/test_dirs.sh

@@ -152,8 +152,6 @@ tests/test.py << TEST
     strcmp(info.name, "..") => 0;
     info.type => LFS_TYPE_DIR;
     lfs_dir_read(&lfs, &dir[0], &info) => 1;
-    printf("nameee \"%s\"\n", info.name);
-    printf("expect \"%s\"\n", "burito");
     strcmp(info.name, "burito") => 0;
     info.type => LFS_TYPE_REG;
     lfs_dir_read(&lfs, &dir[0], &info) => 1;