handle embedded quotes.

Added support for passing a single argument on the shebang line to
pass things like -O and -i.

Fixed bug in handling trailing whitespace in Python command.

--HG--
branch : setuptools-0.6
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/branches/setuptools-0.6%4051487