Add ad-hoc exception for converting fixnums to bytes

Allows
<armedbear@72a5d76>
to work without needing to patch SLIME by performing conversion of
fixnum representation of byte value.  The same should probably be done
for Bignum, and other descendents of LispInteger more systematically.

Resolves <armedbear#141>.

src/org/armedbear/lisp/Fixnum.java

@@ -80,6 +80,12 @@ public Object javaInstance(Class c)
       return Long.valueOf((long)value);
     if (Integer.class.equals(c) || int.class.equals(c))
       return Integer.valueOf(value);
+    if (c.isAssignableFrom(Byte.TYPE)) {
+      // are we in range?
+      return ((java.lang.Number)value).byteValue();
+    }
+
+    int i = 1;
 
     return error(new TypeError("Cannot convert Fixnum to " + c.getName()));
   }