o stay_setuid - sudo will remain setuid if system has saved uids or setreuid(2)
o env_reset - reset the environment to a sane default
o env_keep - preserve environment variables that would otherwise be cleared
No longer use getenv/putenv/setenv functions--do environment munging by hand.
Potentially dangerous environment variables can be cleared only if they
contain '/' pr '%' characters to protect buggy programs.
Moved environment routines into env.c (new file)
