some nsString->nsAutoString cleanup

mailnews/base/util/nsMsgDBFolder.cpp

@@ -201,7 +201,7 @@ NS_IMETHODIMP nsMsgDBFolder::GetCharset(PRUnichar * *aCharset)
 			rv = prefs->CopyCharPref("intl.character_set_name", &prefCharset);
 		}
   
-		nsString prefCharsetStr;
+		nsAutoString prefCharsetStr;
 		if(prefCharset)
 		{
 			prefCharsetStr = prefCharset;
@@ -229,7 +229,7 @@ NS_IMETHODIMP nsMsgDBFolder::SetCharset(const PRUnichar * aCharset)
 	rv = GetDBFolderInfoAndDB(getter_AddRefs(folderInfo), getter_AddRefs(db));
 	if(NS_SUCCEEDED(rv))
 	{
-		nsString charset(aCharset);
+		nsAutoString charset(aCharset);
 		rv = folderInfo->SetCharacterSet(&charset);
 		db->Commit(nsMsgDBCommitType::kLargeCommit);
 	}

mailnews/base/util/nsMsgFolder.cpp

@@ -1702,7 +1702,7 @@ NS_IMETHODIMP nsMsgFolder::SetNumNewMessages(PRInt32 aNumNewMessages)
 NS_IMETHODIMP nsMsgFolder::GetNewMessagesNotificationDescription(PRUnichar * *aDescription)
 {
 	nsresult rv;
-	nsString description("");
+	nsAutoString description("");
 	nsCOMPtr<nsIMsgIncomingServer> server;
 	rv = GetServer(getter_AddRefs(server));
   

mailnews/base/util/nsMsgI18N.cpp

@@ -279,8 +279,8 @@ PRBool nsMsgI18Nstateful_charset(const char *charset)
 PRBool nsMsgI18N7bit_data_part(const char *charset, const char *inString, const PRUint32 size)
 {
   char *aCString;
-  nsString aCharset(charset);
-  nsString outString;
+  nsAutoString aCharset(charset);
+  nsAutoString outString;
   nsresult res;
   
   aCString = (char *) PR_Malloc(size + 1);

mailnews/base/util/nsMsgUtils.cpp

@@ -28,7 +28,6 @@
 #include "nsFileSpec.h"
 #include "nsIServiceManager.h"
 #include "nsCOMPtr.h"
-#include "nsString.h"
 #include "nsIImapUrl.h"
 #include "nsIMailboxUrl.h"
 #include "nsINntpUrl.h"
@@ -50,7 +49,7 @@ nsresult GetMessageServiceProgIDForURI(const char *uri, nsString &progID)
 
 	nsresult rv = NS_OK;
 	//Find protocol
-	nsString uriStr = uri;
+	nsAutoString uriStr(uri);
 	PRInt32 pos = uriStr.FindChar(':');
 	if(pos == -1)
 		return NS_ERROR_FAILURE;