Add Bool method to Capture

Right now, defined captures evaluate to `True`, but empty captures should probably be `False`.
turn WVal into Want + IVal if it's an Int.
need to decont the Int value before isbig_I will work.
cache symbols found in SETTING.
fix $!SETTING cache.
give the Want a .named; add Num and Str.
Merge branch 'wval_to_want' of https://github.com/timo/rakudo into nom
Merge pull request #110 from gerdr/patch-1

Add Bool method to Capture
port List.ACCEPTS back from b

* gets Whatever special handling for lists back.