Replaced sendfiles with a simpler version that uses send instead of viamail.

Replaced sendfiles with a simpler version that uses send instead of viamail.
Also moved it from etc/ to uip/. Updated man pages.

Note: The splitting of large messages by sendfile/viamail/or elsewhere
seems not to be available anymore, although it had been documented in the
man page. Either the man pages don't match the code or I've not found this
function yet.