Print a message from configure if getpass() or crypt() were missing

if the system doesn't support getpass, we still default on the options
that require it which causes a build failure.  instead, only default
enable these when getpass is available.

if the system doesn't support crypt.h/crypt, then ENABLE_SVR_PASSWORD_AUTH
cannot work.  rather than default this to on all the time, do so only when
support for the header is found.

some systems (like android's bionic) do not provide getpass.  you can
disable ENABLE_CLI_PASSWORD_AUTH & ENABLE_CLI_INTERACT_AUTH to avoid
its use (and rely on pubkey auth), but the link still fails because
the support file calls getpass.  do not define this func if both of
those auth methods are not used.

The session.h defines clientsession.cipher_none_after_auth only when
ENABLE_CLI_INTERACT_AUTH is defined, but cli-session.c will always
try to set that member.  export cipher_none_after_auth all the time.

(possibly via authorized_keys(5) restrictions), even when a
pseudo-terminal has been allocated for the session.  In other words,
only display the MOTD when the server starts the user's default shell.

those packets might have been enqueued by set_connect_fds()

Cisco SSH on 15.4(3)M2 or similar can't handle it.

rather than doing ~ expansion

Prepend DROPBEAR for scp.c

Fix warnings

Fix warnings