gitexe list() implemented incorrectly

Taking the Svn implementation as a model, ScmProvider.list() should be implemented as follows:

• The command must directly query the remote repository for files
• A local working copy is unnecessary and if it doesn't exist, the remote repository must not be checked out.
• fileSet.getBasedir() indicates where to run the scm binary. The recommended value is ".".
• fileSet.getFileList() indicates the files to list
• repository indicates the repo URL

Git (among other SCMs) does not support listing remote files, so the command should just fail.

For listing files in a working copy, users should call the ScmProvider.status() method instead.