renamed sendfile() since some systems have a system call named like this -
now the functions are named sendtftp() and recvtftp() instead.

In the Solaris 7 header files for tftp, the th_stuff struct member is an
unsigned short. Trying a typecast here to fix.

prevent warnings on re-defining MIN

use int "subscripts" to prevent warnings from picky compilers

use internal *printf() clones

ifdef for includes, added checking for two not previously checked files (one
being necessary for solaris builds)

First version of the TFTP server. Basic functionality is there.