Use KMimeType::extractKnownExtension() when linking an attachment file

to open, so that it will use the intended file association. 

For example, open a .tar.gz attachment as a .tar.gz file, not as a .gz

BUG:184459

svn path=/trunk/KDE/kdepim/; revision=935825

kmcommands.cpp

@@ -2940,7 +2940,7 @@ QString KMHandleAttachmentCommand::createAtmFileLink() const
 
   KTemporaryFile *linkFile = new KTemporaryFile();
   linkFile->setPrefix(atmFileInfo.fileName() +"_[");
-  linkFile->setSuffix("]."+ atmFileInfo.suffix());
+  linkFile->setSuffix( "]." + KMimeType::extractKnownExtension( atmFileInfo.fileName() ) );
   linkFile->open();
   QString linkName = linkFile->fileName();
   delete linkFile;