space up front and realloc as needed. Changes to the new env pointer
must all be made through insert_env() which now keeps track of
spaced used and allocates as needed.
This greatly simplifies routines that need to do "foreach" type
operations.
o Add new init_envtables() function to set env_check and env_delete
defaults based on initial_badenv_table and initial_checkenv_table
(formerly sudo_badenv_table).
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)
