Fix for `which` on systems that do dumb things.
Fix for `which` on systems that do dumb things.

Fixes #21
mubassirhayat/psysh,bobthecow/psysh,lvht/psysh,damiankloip/psysh,bobthecow/psysh,adetch/psysh,lvht/psysh,barryvdh/psysh,damiankloip/psysh,adetch/psysh,mubassirhayat/psysh,barryvdh/psysh,damiankloip/psysh