- move prompt for password to imap_open()
- don't ask for global password in PREAUTH state
- use socketpair() to create one full-duplex fd in tunnel mode
instead of two half-duplex pipes
- don't set lck.l_pid in fcntl() call (its read-only)
- use F_SETLK instead of F_SETLKW to avoid infinite waiting
- use "$@" in autogen.sh to get proper word expansion
