Distinguish HTTP/1 messages from general HTTP messages:

The version field is moved into message_v1, all public interfaces
are reworked to identify HTTP/1 wire format operations (suffix "_v1")
versus general HTTP.

test/Jamfile

@@ -31,11 +31,12 @@ unit-test core-tests :
 unit-test http-tests :
     main.cpp
     http/basic_headers.cpp
-    http/basic_parser.cpp
+    http/basic_parser_v1.cpp
     http/empty_body.cpp
     http/error.cpp
     http/headers.cpp
     http/message.cpp
+    http/message_v1.cpp
     http/parse_error.cpp
     http/parser.cpp
     http/read.cpp