SPDY: fixed parsing of http version.

There is an error while parsing multi-digit minor version numbers (e.g.
"HTTP/1.10").
SPDY: fixed the DATA frame length handling in case of some errors.

There are a few cases in ngx_http_spdy_state_read_data() related to error
handling when ngx_http_spdy_state_skip() might be called with an inconsistent
state between *pos and sc->length, that leads to violation of frame layout
parsing and resuted in corruption of spdy connection.
Merge pull request #428 from chobits/spdy_bugfix

Spdy bugfix for parsing http version and handling DATA frame length