mm/oom_kill.c (affects lowmemorykiller): make tasks with oom_score_adj = -1000 unkillable
fs/proc/base.c (affects lowmemorykiller): oom_adj -17 triggers oom_score_adj of -1000

Prior to this patch, oom_score_adj was automatically calculated based
on the oom_adj value.
When setting an oom_adj value of the minium value (-17), automatically
set oom_score_adj to its minimum value (-1000) as well.
mm/oom_kill.c (affects lowmemorykiller): prevent changing oom_score_adj if its value is -1000

This should prevent that the Android OS automatically changes
its value if oom_adj -17 or oom_score_adj -1000 were explicitly
set by the user. To gain control over the variable again,
oom_adj has to be set to anything higher than -17.

Also: compare p->signal->oom_score_adj with OOM_SCORE_ADJ_MIN instead
of static value.