Allow {} to remain decoded in URLs in the path and query

Allow {} to remain decoded in URLs in the path and query

This allows things like http://example.com/{1234-5678}?id={abcd-ef01}.
But do not allow it in other parts of the URL. I could allow it in the
fragment, but in the username and password it would be too ugly.

In order to do that, make DecodeReserved use two bits and have
PrettyDecoded set only one of them. That way, toString(PrettyDecoded)
can be distinguished from toString(PrettyDecoded | DecodeReserved),
just as path(PrettyDecoded) can be distinguished from
path(PrettyDecoded & ~DecodeDelimiters).

Also, take the opportunity to avoid decoding the reserved characters
in the query. Keep them encoded as they should be.

Change-Id: I1604a0c8015c6b03dc2fbf49ea9d1dbed96fc186
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>