Fix for excess new lines on 'make login' and other changes to serialdump

I finally found the motivation to search for the bug causing the excess new lines on 'make login'!

The serialdump tool did not set the flags for the serial device correctly (they are uninitialized) and the system may be set to convert all carriage returns (CR) to new lines (LF). Serialdump now always sets the input flags to not convert CR to LF.

Furthermore, I fixed the last broken merge. I also changed some parts of how Mac OS is handled but was not able to test this. Before merging this, a mac user should check wether this works or not.

Last thing is that serialdump now closes with an error when the node gets disconected from the PC, eg. when the USB plug is pulled.