Document the possible presence of multiple variables with the

Document the possible presence of multiple variables with the
same name in http queries, which might confuse the manager.

Replace calls to ast_uri_decode() with a local function that also
replaces '+' with ' ', as this is the normal encoding for
spaces in http requests.
This allows passing cli commands to the manager through the
http interface.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@117295 65c4cc65-6c06-0410-ace0-fbb531ad65f3