Process num of signals received

[giampaolo]

Not sure if it's worth it, but different UNIX variants provide this metric. Keeping this open in order to provide notes on which platforms (and how) this can be determined.

• Solaris: pr_sigs
• Linux: http://stackoverflow.com/questions/5975315/linux-how-to-see-if-a-living-process-has-signal-handlers-set (this is a mask for caught signals, not really what we want)
• BSD: see Process platform specific info #914