forgot one module name that changed

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@137679 65c4cc65-6c06-0410-ace0-fbb531ad65f3

Zaptel-to-DAHDI.txt

@@ -19,6 +19,7 @@ renamed; the new names are:
   app_zapbarge.so -> app_dahdibarge.so
   app_zapras.so -> app_dahdiras.so
   app_zapscan.so -> app_dahdiscan.so
+  codec_zap.so -> codec_dahdi.so
 
 However, in spite of the file name changes, the channels and
 applications provided by these modules can still be used with 'Zap'