Fix a parser bug that was exposed when mixing different runas specs

Fix a parser bug that was exposed when mixing different runas specs
and ! commands.  For example:
    millert        ALL=(daemon) /usr/bin/whoami,!/bin/ls
would allow millert to run whoami as root as well as daemon when it should
just allow daemon.  The problem was that comma-separated commands in
a list shared the same entry on the matching stack.  Now they get
their own entry iff there is a full match.  It may be better to just make
the runas spec persistent across all commands in a list like the user
and host entries of the matching stack.  However, since that is a
fairly major change it should gets its own minor rev increase.