Hopefully fix issue #2662536: Why is launcher being killed?

It looks like there was a subtle bug where Process.setOomAdj() could
return false just because the given process doesn't exist, even though
it is documented to only return false if OOM killing is not supported
at all.  This would cause the activity manager to fall into its code
path of trying to clean up processes itself, which it does a much
poorer problem at.  I am thinking we may be seeing this problem more
now that the activity manager is killing background processes itself
when there are too many of them.

In addition, this change cleans up and reduces some of the logging
around killing processes.

Finally, try to improve process LRU management a bit by taking
into account process dependencies.  Any dependent processes are
pulled up in the LRU list with the processes that is actually
moving.  Also, we bring a process up if someone accesses its content
provider.

Change-Id: I34ea161f839679345578ffe681e8d9c5d26ab948