. create signals-related struct message type to store sigset_t
directly
. create notify-specific message types, so the generic NOTIFY_ARG
doesn't exist anymore
. various related test expansions, improvements, fixes
. add a few error-checks to sigismember() calls
. rename kernel call specific signals fields to SYS_*
Change-Id: I53c18999b5eaf0cfa0cb25f5330bee9e7ad2b478