tree.c

More error return wrapping.

* subversion/libsvn_fs_base/bdb/bdb-err.c,
subversion/libsvn_fs_base/bdb/changes-table.c,
subversion/libsvn_fs_base/bdb/env.c,
subversion/libsvn_fs_base/bdb/lock-tokens-table.c,
subversion/libsvn_fs_base/bdb/locks-table.c,
subversion/libsvn_fs_base/bdb/txn-table.c,
subversion/libsvn_fs_base/dag.c,
subversion/libsvn_fs_base/fs.c,
subversion/libsvn_fs_base/lock.c,
subversion/libsvn_fs_base/reps-strings.c,
subversion/libsvn_fs_base/revs-txns.c,
subversion/libsvn_fs_base/tree.c,
subversion/libsvn_fs_fs/fs_fs.c,
subversion/libsvn_fs_fs/tree.c:
Add some calls to svn_error_return().