ARGV_t const pendantry

ARGV_t const pendantry
- const on typedef'ed ARGV_t doesn't mean a thing, add a new,
  (exec* compatible) ARGV_const_t and use where appropriate consistently in
  argv.h, rpmcli.h etc
- popt's argv const is the wrong way around for exec() family, add explicit
  ARGV_t casts on popGetArgs() uses where needed
- compiler silence, aaahh...