luci-base: urlencode: encode all except unreserved characters.

As per http://tools.ietf.org/html/rfc3986#section-2.3

   Characters that are allowed in a URI but do not have a reserved
   purpose are called unreserved.  These include uppercase and lowercase
   letters, decimal digits, hyphen, period, underscore, and tilde.

      unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

modules/luci-base/luasrc/http/protocol.lua

@@ -72,7 +72,7 @@ function urlencode( str )
 
 	if type(str) == "string" then
 		str = str:gsub(
-			"([^a-zA-Z0-9$_%-%.!*'(),])",
+			"([^a-zA-Z0-9$_%-%.%~])",
 			__chrenc
 		)
 	end