Ignore "--alternative-project <prj>" if it is equal to the wc's project

Without this change, using "--alternative-project <prj>" in combination
with "--multibuild-package <flavor>" yields to unexpected results (from
a user's point of view). Note that this may break existing (artificial)
workflows (e.g., using --alternative-project to ignore the package
meta's debuginfo flag), but these workflows should be rare and there
are options to achieve the same.

Fixes: #376 ("osc build -M something does not work with
--alternative-project")

osc/commandline.py

@@ -6170,6 +6170,14 @@ Please submit there instead, or use --nodevelproject to force direct submission.
         if len(args) > 3:
             raise oscerr.WrongArgs('Too many arguments')
 
+        project = None
+        try:
+            project = store_read_project(os.curdir)
+        except oscerr.NoWorkingCopy:
+            pass
+        if project == opts.alternative_project:
+            opts.alternative_project = None
+
         args = self.parse_repoarchdescr(args, opts.noinit or opts.offline, opts.alternative_project, False, opts.vm_type, opts.multibuild_package)
 
         # check for source services