The single-table tablespaces loaded twice during backup

Regression in lp:~sergei.glushchenko/percona-xtrabackup/xb21-bug932623:

2012-07-31 13:58:32: xb_incremental.sh: ===> /home/laurynas/percona/src/xb21-bug932623/test/../src/xtrabackup --no-defaults --datadir=/home/laurynas/percona/src/xb21-bug932623/test/var1/data --backup --target-dir=/home/laurynas/percona/src/xb21-bug932623/test/var1/data/full
/home/laurynas/percona/src/xb21-bug932623/test/../src/xtrabackup version 2.0.0 for Percona Server 5.1.59 unknown-linux-gnu (x86_64) (revision id: undefined)
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /home/laurynas/percona/src/xb21-bug932623/test/var1/data
xtrabackup: Target instance is assumed as followings.
xtrabackup: innodb_data_home_dir = ./
xtrabackup: innodb_data_file_path = ibdata1:10M:autoextend
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 2
xtrabackup: innodb_log_file_size = 5242880
120731 13:58:32 InnoDB: Warning: allocated tablespace 10, old maximum was 9
120731 13:58:32 InnoDB: Warning: trying to init to the tablespace memory cache
InnoDB: a tablespace 10 of name './incremental_sample/test.ibd',
InnoDB: but a tablespace 10 of the same name
InnoDB: already exists in the tablespace memory cache!
InnoDB: We assume that InnoDB did a crash recovery, and you had
InnoDB: an .ibd file for which the table did not exist in the
InnoDB: InnoDB internal data dictionary in the ibdata files.
InnoDB: We assume that you later removed the .ibd and .frm files,
InnoDB: and are now trying to recreate the table. We now remove the
InnoDB: conflicting tablespace object from the memory cache and try
InnoDB: the init again.

The problem is that the branch introduces xb_data_files_init() which is called from, among other places, xtrabackup_backup_func(). Both these functions call fil_load_single_table_tablespaces(), resulting in these messages. Fix is trivial, only 2.1 is affected.