TODO

* The DISPLAY setting should be honoured by the pinentry applications
  using XFree86.  This implies reconfiguring the underlying toolkit,
  is this always possible?
  (This is not so important, as pinentry is always restarted.)

* The Qt and curses PIN entry should support enhanced mode (when it is
  implemented in gpg-agent).  We need to agree on a protocol to use
  anyway.

* The Qt pinentry uses QT's private QTextLayout.

* Set the max length of password globally (dynamically in protocol?).

* A heartbeat status message should be sent every few seconds, so that
  the gpg-agent is better able to cope with jammed pinentries.

* The gtk+-2 pinentry needs auditing.

* Implement the one_button feature in Qt.

* The format of the Assuan protocol description should be changed to
  the one used by GnuPG.
  
* The SETTITLE command is only implemented for GTK+-2