Bug#896929: java.ext.dirs is gone

[debian at fau.xxx]

I traced this problem to RXTXCommDriver.java:415:
System.getProperty("java.ext.dirs") comes back null. It's illegal to
-Djava.ext.dirs on Java 10/11. The easiest fix appears to be to add a
second argument (default value) of the empty string, which makes the
code/loop a noop. That, or try and switch it over to classpath? It's
unclear to me where it's expecting to find a property file file, but
maybe it does in some setups.

Debugging is a lot easier if you add e.printStackTrace(); to all three
/thrown while loading/ catch and discard blocks.

Also, the package fails to build for me on Ubuntu's Java "11" (i.e. Java
10 in a weird package name), due to javah removal.

Chris.