patman: Convert 'Series-xxx' tag errors into warnings

If the Series-xxx tag is not recognised patman currently reports a fatal
error. This is inconvenient if a new feature is later added to patman that
an earlier version does not support.

Report a warning instead, to allow the user to take action if needed, but
still allow operation to proceed.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/patman/patchstream.py

@@ -114,7 +114,9 @@ class PatchStream:
             self.in_section = name
             self.skip_blank = False
         if self.is_log:
-            self.series.AddTag(self.commit, line, name, value)
+            warn = self.series.AddTag(self.commit, line, name, value)
+            if warn:
+                self.commit.warn.append(warn)
 
     def _add_to_commit(self, name):
         """Add a new Commit-xxx tag.

tools/patman/series.py

@@ -59,6 +59,9 @@ class Series(dict):
             line: Source line containing tag (useful for debug/error messages)
             name: Tag name (part after 'Series-')
             value: Tag value (part after 'Series-xxx: ')
+
+        Returns:
+            String warning if something went wrong, else None
         """
         # If we already have it, then add to our list
         name = name.replace('-', '_')
@@ -78,9 +81,10 @@ class Series(dict):
             else:
                 self[name] = value
         else:
-            raise ValueError("In %s: line '%s': Unknown 'Series-%s': valid "
+            return ("In %s: line '%s': Unknown 'Series-%s': valid "
                         "options are %s" % (commit.hash, line, name,
                             ', '.join(valid_series)))
+        return None
 
     def AddCommit(self, commit):
         """Add a commit into our list of commits