Be exact about the number of spaces in the header.

Also fixes changes files that warn on this.

scripts/maint/lintChanges.py

@@ -31,7 +31,7 @@ def lintfile(fname):
     lines = contents.split("\n")
     isBug = ("bug" in lines[0] or "fix" in lines[0])
 
-    if not re.match(r'^ +o (.*)', contents):
+    if not re.match(r'^[ ]{2}o (.*)', contents):
         warn("header not in format expected")
 
     contents = " ".join(contents.split())