bundle2: force the first char of parameter to be an letter. We need a case sensitive character to convey mandatory/advisory parameter semantic in a later patches.

bundle2: refuse empty parameter name The bundle2 now raise value error when seeing invalid parameter names. The first introduced rules is: no empty parameter. The test extension is improve to properly abort when ValueError are encountered.

bundle2: urlunquote stream parameter name and value during unbundling Align to new escaping used during bundling.