LU-118 Workaround for race causing assertion failure in clear_inode()

LU-118 Workaround for race causing assertion failure in clear_inode()

This patch is just a *workaround* to avoid a race found in recent
kernel causing the following assertion in clear_inode():
BUG_ON(inode->i_data.nrpages).
The race can still occur when truncate_inode_pages() & clear_inode()
are called directly by the VFS, but the problem should be harder to
reproduce.
A more complete fix is considered for 2.x.

Change-Id: If0df4b1cba00de7cf43f1b3510d54d35525c5e14
Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/475
Tested-by: Hudson
Reviewed-by: Jinshan Xiong <jay@whamcloud.com>
Reviewed-by: Andrew Perepechko <andrew_perepechko@xyratex.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>