Added a force charset override UI, bug 43101, r=mscott.

mailnews/base/prefs/resources/content/pref-viewing_messages.xul

@@ -15,7 +15,7 @@
 
   <script language="javascript">
   <![CDATA[
-    _elementIDs = ["mailFixedWidthMessages", "mailQuotedStyle", "mailQuotedSize", "wrapLongLines", "displayGlyph", "displayStruct", "mailCitationColor", "sendDefaultCharsetList"];
+    _elementIDs = ["mailFixedWidthMessages", "mailQuotedStyle", "mailQuotedSize", "wrapLongLines", "displayGlyph", "displayStruct", "mailCitationColor", "sendDefaultCharsetList", "forceCharsetOverride"];
 
     function Startup()
     {
@@ -130,6 +130,9 @@
       </template>
     </menulist>       
     </box>    
+  <checkbox id="forceCharsetOverride" value="&forceCharsetOverride.label;" accesskey="&forceCharsetOverride.accesskey;"
+            pref="true" preftype="bool" prefstring="mailnews.force_charset_override" 
+            prefattribute="checked"/>
 	</titledbox>
 	  
 </window>

mailnews/base/prefs/resources/locale/en-US/pref-viewing_messages.dtd

@@ -41,6 +41,8 @@ Rights Reserved.
 <!ENTITY languages.label				  "Languages">
 <!ENTITY coding.label					  "Use the following character coding as the default for viewing messages:">
 <!ENTITY sendDefaultCharset.label         "Character Coding:">
+<!ENTITY forceCharsetOverride.label       "Apply default to all messages (ignore charset specified by MIME header).">
+<!ENTITY forceCharsetOverride.accesskey   "i">
 <!ENTITY fixedWidth.label                 "Fixed width font">
 <!ENTITY fixedWidth.accesskey             "x">
 <!ENTITY variableWidth.label              "Variable width font">