subrepo: only retrieve the first two components of the Git version This makes the version detection compatible with Git versions like '1.9-rc0'. We only cared about the first two components of the version anyway.

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.