fix string range to have full unicode range (up to 10FFFF).

fix string range to have full unicode range (up to 10FFFF).
add test for string range.

test has minor failure: after loop the index == len(s); should be len(s)-1
in this case.  according to spec, vars are left at position at last
iteration.

R=ken,rsc
DELTA=259  (161 added, 96 deleted, 2 changed)
OCL=27343
CL=27343