#610 Make Osm2GpsMid ask jarsigner password

[Jyrki Kuoppala]

Though asking and feeding the passphrase to jarsign could have some
complications:

* either we would feed it blindly to jarsigner; don't know if the run would
hang then
* or we'd have to parse jarsigner output to get a cue when to feed the
password, making Osm2GpsMid dependent on certain jarsigner output (might
stop working e.g. if someone uses a jarsigner in a different language,
don't know if sun/oracle have localized it though)