gdb/copyright.py: Do not forget to remind about MULTIPLE_COPYRIGHT_HEADERS

There is a small logical error in the part of the script that
dumps the list of files in BY_HAND + MULTIPLE_COPYRIGHT_HEADERS
but only checkis the contents of BY_HAND. The issue becomes
apparent as soon as BY_HAND is empty. Prevent this from happening
by treating the two lists separately, as this allows us to provide
a more informative message in the case of MULTIPLE_COPYRIGHT_HEADERS.

gdb/ChangeLog:

        * copyright.py (main): Dump the contents of
        MULTIPLE_COPYRIGHT_HEADERS (separately) from BY_HAND,
        even if BY_HAND is empty.

gdb/copyright.py

@@ -150,11 +150,20 @@ def main ():
     update_files (update_list)
 
     # Remind the user that some files need to be updated by HAND...
+
+    if MULTIPLE_COPYRIGHT_HEADERS:
+        print
+        print("\033[31m"
+              "REMINDER: Multiple copyright headers must be updated by hand:"
+              "\033[0m")
+        for filename in MULTIPLE_COPYRIGHT_HEADERS:
+            print "  ", filename
+
     if BY_HAND:
         print
         print "\033[31mREMINDER: The following files must be updated by hand." \
               "\033[0m"
-        for filename in BY_HAND + MULTIPLE_COPYRIGHT_HEADERS:
+        for filename in BY_HAND:
             print "  ", filename
 
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