Added a "Quit" option to Savant's File menu. Factored out the Close
option in doing so.
Exceptions in many action listeners are now handled by
org.thdl.util.ThdlActionListener or org.thdl.util.ThdlAbstractAction.
Many exceptions that we used to just log now optionally cause aborts.
This option is on by default for developers using 'ant savant-run'-style
targets, but it is off for users.
An erroneous CLASSPATH now causes a useful error message in almost
all situations.
Fixed some typos and bad links in Javadoc comments.
Added a simple assertion facility, but the overhead is suffered even in
release builds.
Factored out the code that sets up log files like savant.log and jskad.log.
