HTTP: remove auto-decoding of UTF-8 content (cc#2027)

When READing via HTTP (without `/string` or `/lines`), no longer auto-decode UTF-8 encoded content to a `string!`. Always return a `binary!` instead.

The auto-decoding feature removed by this commit lead to brittle code, when developers testing with a site that by chance returned a string! were lead to believe that an http:// READ always returns a `string!`.

This fixes [CureCode issue #2027](http://issue.cc/r3/2027).

Fix as originally suggested by Graham Chiu.