[PATCH] allow callers of seq_open do allocation themselves

Allow caller of seq_open() to kmalloc() seq_file + whatever else they
want and set ->private_data to it.  seq_open() will then abstain from
doing allocation itself.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>