raise http headers limit for proxy-auth
add cert-ignore-hostname, use std::string for proxy-auth header

Conflicts:
	src/shrpx_spdy_downstream_connection.cc
another proxy-auth header fix

Conflicts:
	src/shrpx_spdy_downstream_connection.cc
another trial :(

Conflicts:
	src/shrpx_spdy_downstream_connection.cc
another another try