Allow user to read the result of wget.

Several retro targets clear the screen after program termination so allow user to read the result.
Be consistent with tab chars in Makefiles.
Moved from last cc65 release (2.13.3) to recent cc65 snapshot (2.13.9).

Relevant cc65 changes...

General:
- The compiler generates "extended" dependency info (like gcc) so there's no need for postprocessing whatsoever :-)
- The linker is very pernickety regarding the ordering of cmdline options so a custom linker rule is necessary :-(

Apple2:
- The various memory usage scenarios aren't specified anymore via separate linker configs but via defines overriding default values in the builtin linker config.

Atari:
- The builtin linker config allows to override the start addr so there no more need for a custom linker config.
- The C library comes with POSIX directory access. So there's no more need for for a custom coding.

CBM:
- The C library comes with POSIX directory access. So there's no more need for for a custom coding.
The recent cc65 snapshot yields somewhat small programs so we can move back to the MTU size used before.
Reduced program size.

On the C128 the custom PFS code doesn't add functionality (as it does with IDE64 support on the C64) but is "only" smaller than the POSIX file i/o code in the C library. But the POSIX directory access code in the C library relies on the POSIX file i/o code anyway so there no point in additionally adding the PFS code to the FTP program.
Add mesh_ready() to mesh
mesh_ready checkes whether a packet is queued. This allows to avoid
packet loss at application level.
Fix indention on mesh* using tools/contiki-indent and fix the pointer-issue manually