BTP 6.4.0:

- Unify all code leading to (success AND failure) exit 
  (so everithing can get closed and freed correctly).
- Collect all tips and documentation, and write a proper tutorial.
- Re-implement imagebutton support.
- Make the error message appear at the same coordinates that the btp window
  occupies, not an absolute position.
- Is there really no way to make Fl_Multiline_Output break lines automatically?
- Allow adequate combinations of hardbuttons (may be also hard/soft ...?)
- Support the SEND_START / SEND_STOP feature of rc.
- Separate the definition of Macros and Buttons 
  (This may lead to .ini file incompatibilities...).
- Allow "background" labels (with no button associated).

DONE!
- Add support for compiling a native btp in the makefile.
- Clean up handling of a missing remote.ini.
- Implement IR-Remote multiviews.
- Allow multi-line text in buttons
