Convert Lisp truth values to Java equivalents in JCALL/JSTATIC.
We now convert CL:T and CL:NIL to JAVA:+TRUE+ and JAVA:+FALSE+
respectively when invoking JVM methods through the JAVA package,
establishing the "natural" equivalence for boolean truth values. This
may break some existing usage in that previously CL:NIL was converted
to a Java 'null' reference. Users now need to specify JAVA:+NULL+
explicitly when desiring to pass 'null' Java references as an argument
in invoking JVM methods.