shelltest: confirm that 'local' is definitely available.
shelltest: confirm that 'local' is definitely available.

Supposedly it's not POSIX, but every shell I have seems to support it, so
let's just reject any that don't.  And like magic, anybody using redo can
now count on the 'local' builtin working.

rowhit/redo,apenwarr/redo,dinkelk/redo-python,pombredanne/redo,rowhit/redo,pombredanne/redo,pombredanne/redo,rowhit/redo,rowhit/redo,dinkelk/redo-python,dinkelk/redo-python,apenwarr/redo,pombredanne/redo,apenwarr/redo,dinkelk/redo-python,apenwarr/redo