MINOR: http: Add the "language" converter to for use with accept-language

MINOR: http: Add the "language" converter to for use with accept-language

language(<value[;value[;value[;...]]]>[,<default>])

	 Returns the value with the highest q-factor from a list as
	 extracted from the "accept-language" header using "req.fhdr".
	 Values with no q-factor have a q-factor of 1. Values with a
	 q-factor of 0 are dropped. Only values which belong to the
	 list of semi-colon delimited <values> will be considered. If
	 no value matches the given list and a default value is
	 provided, it is returned. Note that language names may have
	 a variant after a dash ('-'). If this variant is present in
	 the list, it will be matched, but if it is not, only the base
	 language is checked. The match is case-sensitive, and the
	 output string is always one of those provided in arguments.
	 The ordering of arguments is meaningless, only the ordering
	 of the values in the request counts, as the first value among
	 multiple sharing the same q-factor is used.

	 Example :

	     # this configuration switches to the backend matching a
	     # given language based on the request :

	     acl de req.fhdr(accept-language),language(de;es;fr;en) de
	     acl es req.fhdr(accept-language),language(de;es;fr;en) es
	     acl fr req.fhdr(accept-language),language(de;es;fr;en) fr
	     acl en req.fhdr(accept-language),language(de;es;fr;en) en
	     use_backend german  if de
	     use_backend spanish if es
	     use_backend french  if fr
	     use_backend english if en
	     default_backend choose_your_language