* build.sh completely cleaned wrt serial & -s

* build.sh completely cleaned wrt serial & -s
- can specify either -s <> or serial anywhere in the type
- supports -s default
- output filenames fixed, does not mention the console characteristics when default is used, duplicate serial fixed
* build.sh supports a new -o option, so the caller can specify the output
* GetBootMedium uses this new -o option
* GetBootMedium now has 3 known options serial[:console] cramfs partition
* GetBootMedium cowardly refuses options when deailng with floppy or generic images

haven't looked into planetlab's www module - so long as the web only supports iso/usb this should run fine