Don't mess with pidfile if it has our pid

If you HUP gmond and you ran it with -p it will reexec itself, keeping its
pid, read the pidfile, find a process with its pid running and exit (so as
to prevent two gmonds running at once).  This isn't correct as it should
just keep running and not do anything with its pidfile.
Add a "summarized_metrics" option.

This feature works notionally the same as unsummarized_metrics, except
it serves as a list of metrics to summarize explicitly (instead of
ignoring metrics to leave out). This can be useful when aggregating
large numbers of metrics where only a very small number of metrics are
actually useful when summarized.

Note that while unsummarized_metrics works for filtering cluster / host
/ metrics, summarized_metrics only changes the behavior of summaries.
Merge pull request #127 from dhobsd/dho/summarized-metrics

Add a "summarized_metrics" option.
Merge pull request #29 from shufgy/master

Don't die when you HUP gmond -p