Fix bug in 'take' on infinite streams for symbolic simulator
Fix bug in 'take' on infinite streams for symbolic simulator

Previously, 'take'ing a finite prefix of an infinite stream would
incorrectly yield a 'VStream' value, which would normally indicate
an infinite result. Now it correctly returns a 'VSeq' value.

GaloisInc/cryptol,TomMD/cryptol,TomMD/cryptol,ntc2/cryptol,GaloisInc/cryptol,GaloisInc/cryptol,TomMD/cryptol,TomMD/cryptol