lwip 1.3.1 package

Hi John

I have updated my lwIP package with the final 1.3.1 release. There are 
changes in two areas, and I wonder how to tackle them:

1. SLIP polling support

I changed the SLIP netif to support polling, so it does not need to run 
in it's own thread when resources are low. I submitted the patch to lwip 
quite a bit of time ago, but there were no reactions:

http://savannah.nongnu.org/bugs/?26397

I could of course remove my changes, but then the eCos package will not 
support SLIP in the simple/polled mode. So I'd also have to change some 
of the glue code. I would rather like to keep SLIP polling support in.

2. PPP

There are quite a bit of changes I made to the PPP code:

* put code more in line with lwip coding style (mostly renaming)
* added a simple chat component, to connect a modem to the peer
* added support for PPP dumps (wireshark)
* added polling support
* added an eCos testcase (only for simple/polled mode)

If I restore the original PPP code as suggested, I will also have to 
adapt the glue code and configuration. I would remove the testcase and 
generally mark PPP as experimental. The other way would be to try and 
clean PPP more up, and get the changes commited to lwip, but then we 
would have to wait for another release.

What's your suggestion?

Simon