SSL: logging level of "inappropriate fallback" (ticket #662).

Patch by Erik Dubbelboer.
SPDY: improved debug logging of inflate() calls.
SPDY: fixed check for too long header name or value.

For further progress a new buffer must be at least two bytes larger than
the remaining unparsed data.  One more byte is needed for null-termination
and another one for further progress.  Otherwise inflate() fails with
Z_BUF_ERROR.