[CVE-2011-2203] hfs malicious filesystem fix

[Andy Whitcroft]

CVE-2011-2203
	Clement Lecigne reports a filesystem which causes a kernel oops in
	hfs_find_init() trying to dereference sb->ext_tree which is NULL.

Fixes for this issue have hit precise via upstream.  Following this
email are two patches, one for hardy and lucid/fsl-imx51, the other for
lucid, maverick, maverick/ti-omap4, natty, natty/ti-omap4, and oneiric.
These are both trivial cherry-picks though in the hardy, lucid/fsl-imx51
the original check replaced in this patch is missing.

Proposing for hardy, lucid/fsl-imx51, lucid, maverick, maverick/ti-omap4,
natty, natty/ti-omap4, and oneiric.

-apw