Fixes for #100 (stall of transmit logic) and #102 (packet corruption)

[ntruchsess]

Fixes for #100 and #102

(unfortunally these fixes come with a penalty of 116 bytes flash though...)

[DrewJaworskiRIS]

Are you still planing to merge this request, or do you need more testing to be sure?

[ntruchsess]

While it seems to work It still needs a bit of refactoring as it implements a retransmit-logic that is useful for UDP packets but unnecessary for TCP (as TCP will retransmit lost packages anyway). Simplifying this part should result in smaller footprint. Unfortunately I'm quite busy these days - hope to have time for this issue during winter-holidays. If you feel you might contribute please go ahead :-)

[GunterO]

Well, this version is running rock solid for quite some time now on my projects, I think you nailed the problem. Thanks for all your effort Norbert! And, happy X-mass :-)