The tftpd test server now logs all received options and thus all TFTP
test cases need to match them exactly.
Extended test 283 to use and verify --tftp-blksize.
I've now made TFTP "connections" not being kept for re-use within libcurl.
TFTP is UDP-based so the benefit was really low (if even existing) to begin
with so instead of tracking down to fix this problem we instead removed the
re-use. I also enabled test case 1099 that I wrote a few days ago to verify
that this change fixes the reported problem.
