Http_headers: add pragma.

src/http/http_headers.ml

@@ -48,6 +48,7 @@ let if_unmodified_since = name "If-Unmodified-Since"
 let if_range = name "If-Range"
 let last_modified = name "Last-Modified"
 let location = name "Location"
+let pragma = name "Pragma"
 let server = name "Server"
 let set_cookie = name "Set-Cookie"
 let status = name "Status"

src/http/http_headers.mli

@@ -55,6 +55,7 @@ val if_unmodified_since : name
 val if_range : name
 val last_modified : name
 val location : name
+val pragma : name
 val server : name
 val set_cookie : name
 val status : name