bug#6300: browse-url-encode need to encode more

[Chong Yidong]

Lars Magne Ingebrigtsen <larsi@gnus.org> writes:

> Lennart Borgman <lennart.borgman@gmail.com> writes:
>
>>> Is there any reason space shouldn't be quoted as %20 instead?  I.e.,
>>> just add it to the regexp there at the end?
>>
>> Yes. Readability.
>
> But if I remember correctly, it's not, strictly speaking, er, correct.
>
> Space can be "+" in the query part of an URL, but should be %20
> elsewhere.

I committed the change with spaces percent-encoded.