Committing patch by Thomas Fischer

The patch comes from bugzilla

Thomas writes;
I will attach a patch for KOffice 2.1.2 to this bug report which improves the "Export to PDF" function in the following aspects:
- If the current document was saved before, suggest the same file name here, too, but replace the file ending with ".pdf". This mimics the behavior of OpenOffice
- The KFileDialogs list of file types is now set via mime types, not a list of extensions
- The dialog's caption is rewritten to match the menu item