Espruino Wifi Socket recovery

Ok, should now be fixed on cutting edge builds.

It seems there were two issues:

• If you got two separate data packets in a single callback it only handled the first and then passed the second on as a normal unhandled line
  
• The socket write function waited for "> ", but then after it got it, it accidentally cleared the entire contents of buffer after that (which could have contained the start of +IPD)
  
  

edit: There is still some strangeness (which has been a longstanding thing with Espruino) where if you write a bunch of stuff to USB and you write a lot of stuff to Serial, occasionally you end up with a duplicated character. It means that if you turn on wifi.debug you can still hit reliability issues even though it'd be rock solid without it :(