When installing the `serial` package (in contrast to `pyserial`)
the pyterm script will print a cryptic error message and fail.
This is because both packages, though unrelated, expose a `serial`
package (whereas pyserial should expose `pyserial`).
This change catches the error and might save some precious lifetime
of unsuspecting RIOT users, such as myself.
The default behaviour only appreciates the LF character (unix style).
The pyterm switch -nl/--newline can be used to specify the newline combination of CR/NL.
Possible values are CR, NL, CRNL and NLCR. Default is NL.
For the MSB-A2 the DTR and RTS pins have to be pulled down over the
serial interface in the beginning. (This is required because the Linux
usbserial driver pulls them up when initializing the device which set
the node into reset mode.) Since this is not necessary on most other
platforms and might even cause problems, it's better to make this an
optional behavior of pyterm.
