Use unquote_plus() to get correct request arguments

[JK-de]

On typing "a b" in a form <input> the argument arrives at handler with "a+b" The '+' is a symbol for space while transport and should be replaced on reading header lines.

If you type in the form element:

[a b]

you get with actual version a HTTP-GET or HTTP-POST:

"<addr>/?k=a+b"

you get a dict with:

{'k': 'a+b'}

With this change you get a correct dict with:

{'k': 'a b'}

[jczic]

Yes exactly :) Thanks !

[petrkr]

This issue appeared again. Was introduced back by commit 8a2130df7a132ee9190018415dfa0c72f2d9f973