hush: initial trap support

[Mike Frysinger]

i felt like learning something new and so i took a stab at implementing the 
trap interface.  seems to work fine for me, but i'm not familiar with the 
signal code (job/etc...) in hush, so i took a more conservative approach.  
when a trap is first set, the current sigaction is saved.  then when the trap 
is cleared, the previous sigaction is restored.  this means i need a sigaction 
struct for every signal which adds up pretty quickly.  this patch has overhead 
of 5k data just for this crap.  so clearly this isnt the route we want to go.  
on the flip side, it only(?) adds about 800bytes of code.
-mike
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