Backported ZCache mechanism from Linux Kernel 3.9.11
Remove unused files
Adapt ZCache from kernel 3.9 to kernel 3.0
Backport Frontswap frontend mechanism from kernel 3.9
Backport cleancache from kernel 3.9
Add zswap backend from Linux kernel 3.11
Update frontswap to Linux kernel 3.11
Update cleancache to Linux kernel 3.11
Update zcache to Linux kernel 3.11
Update zsmalloc to Linux kernel 3.11
Tweaked fs/dache, mm/page-writeback and mm/page_alloc

Signed-off-by: Willi Ye <williye97@gmail.com>

Conflicts:
	mm/page-writeback.c
	mm/page_alloc.c