Moved PyPi-related picosat installer code in the download function to avoid the need for internet connection on --check and --env commands
Moved PyPi-related picosat installer code in the download function to avoid the need for internet connection on --check and --env commands

This addresses issue #384

pysmt/pysmt,agriggio/pysmt,agriggio/pysmt,pysmt/pysmt