Enforce label uniqueness in ProjectConfig and ProjectState

Within a single project, it is an error to specify two different
labels that differ only in case. (Multiple [label "Foo"] sections with
the same case are automatically collapsed by JGit.)

Between projects, it is valid to override a label "Foo" in a parent
project with a label "foo" in a child.

Change-Id: Ica6b990feefb272d1675c0f006162afbe51335b5

gerrit-server/src/main/java/com/google/gerrit/server/project/ProjectState.java

@@ -347,9 +347,10 @@ public class ProjectState {
     Collections.reverse(projects);
     for (ProjectState s : projects) {
       for (LabelType type : s.getConfig().getLabelSections().values()) {
-        LabelType old = types.get(type.getName());
+        String lower = type.getName().toLowerCase();
+        LabelType old = types.get(lower);
         if (old == null || !old.canOverride()) {
-          types.put(type.getName(), type);
+          types.put(lower, type);
         }
       }
     }