changable at runtime (and on a global, per-host and per-user basis).
Both the names and the internal representation are still subject to change.
It was necessary to make sudo_user.runas but a char ** instead of a
char * since this value can be changed by a Defaults line. There is a
similar (but more complicated) issue with sudo_user.prompt but it
is handled differently at the moment.
Add a "-L" flag to list the name of options with their descriptions. This
may only be temporary.
Move some prototypes to parse.h
Be much less restrictive on what is allowed for a username.
