Add a really tacky fix for a large bug somewhere in Scons' Java scanner.

The nature of the bug is really complex; it appears to have its roots in the fact that
Scons (apparently) scans for Java source files whilst PARSING the SConstruct file, which
means that it works from a clean directory (ie: scons -c && scons always builds correctly).

However, if you issue scons && scons, the second attempt will fail because the scanner detects
STS.java in org/lsfn/console_pc/ and then somehow does NOT detect that STS.java belongs
in that package, deciding instead that it has no package, and thus its class file is
build/STS.class, rather than the correct build/org/lsfn/console_pc/STS.class

Weird. Anyway, fixed by simply rejecting non-existent files from the CLASS_FILES list.