Adding an option to auto-detect common short date format,

bug 98144, r=ducarroz, sr=sspitzer.

mailnews/base/resources/locale/en-US/messenger.properties

@@ -201,9 +201,14 @@ mail.addr_book.show_phonetic_fields=false
 # 4: mm/yyyy/dd
 # 5: dd/mm/yyyy
 # 6: dd/yyyy/mm
-mailnews.search_date_format=3
-# separator for search date (e.g. "/", "-")
-mailnews.search_date_separator=/
+#
+# 0: auto-detect the current locale format
+#    a separator has to be either '/', '-', '.' and the year in Chistian year
+#    otherwise mm/dd/yyyy (option 3) is used
+#
+mailnews.search_date_format=0
+# separator for search date (e.g. "/", "-"), or empty when search_date_format is zero
+mailnews.search_date_separator=
 
 # offline msg