backport lowmemorykiller from CAF msm-3.4

this improves low memory behaviour greatly due to accounting for
lowmem_reserve as well as shmem pages.
Merge pull request #2 from plaguedbypenguins/cm-10.1-for-konstat

backport lowmemorykiller from CAF msm-3.4
Merge remote-tracking branch 'upstream/cm-10.1' into cm-10.1