USB and Serial Port add-ons added

Hi,

have commited the USB Port transport add-on contributed by Andreas Benzler
and my untested Serial Port add-on (which is a slightly modified copy of the 
Parallel Port
add-on).

BTW it seems BeOS R5 supports one connected USB printer only. Can somebody
verify this?

I have a more than a have year old copy of the cvs repository and since I 
updated to the latest version of jam, Jamfile and Jambase in the root 
directory, 
I can not build anything, because jam crashes

I get this
warning: unknown rule SystemMain 
4 times
and then jam crashes (it seems with a stack overflow).
The stack trace repeats these lines some thousand times:
fcfe5254   8001153d  evaluate_rule + 00000171
fcfe5278   8001138c  compile_rule + 000000b8
fcfe52cc   8001160a  compile_rules + 0000007e
fcfe52e4   80009a61  parse_file + 00000071
fcfe5328   80010fde  compile_include + 000000d2 

Philippe or whoever reads this, please check that the checked in 
source code builds without errors 
(current/src/add-ons/print/transports/usb_port, serial_port, parallel_port).

TIA
- Michael