New option for pg_basebackup, to specify a different directory for pg_xlog

Please find attached the patch, for adding a new option for pg_basebackup, to specify a different directory for pg_xlog.

Design

A new option: "xlogdir" is added to the list of options for pg_basebackup. The new option is not having an equivalent short option letter.
This option will allow the user to specify a different directory for pg_xlog.

The format for specifying a different directory will be: --xlogdir=/path/to/xlog/directory

eg:
pg_basebackup --xlogdir=/home/pg/xlog -D ../dataBaseBackUp

When user specifies a xlog directory, it creates a symbolic link from the default directory to the user specified directory.
User can give only absolute path for the xlog directory. This option will work only if the format for the backup is 'plain'.

Please provide your feedback / suggestions

Regards,
Hari babu.