Autodetect serial port

Hi Ricardo,

thanks for all your work with jobexftp, here are two commits for review, comments welcome!
##### Switching to nrjavaserial
I have had a lot of problems with the serial IO part, same as described by Chris [here] (https://github.com/3esmit/JObexFTP/issues/3). Original rxtx is completely useless on linux (SIGSEGV), cloudhopper frequently results in 0pointers in getall(). Next I tried the create-lab-commons and NRJavaSerial forks, both worked much better in windows. In linux, I did not get any of them to work, might try the nasty-serial branch next (another alternative could be purejavacomm, but that would need some code adjustement) 

In  the end I settled with NRjavaserial, as it is more recent and active. Another big advantage over the cloudhopper builds is that native libs are self-deployed.
##### Serial port autodetection
Basically,  I assume a TC65 to be detected when setting the device to AT_Mode does not throw a IO/NoSuchPort/PortInUse exception. If a portname is specified as argument, this port is checked first. Discovering serial ports does work correclty for me on linux (checks ttyS0 and usb adapters at ttyUSBx). There are some drawbacks (see commit message).