Finished the PDP-10 Move Magnitude opcodes, along with the Push Down and Pop Up opcodes (uncovering some SIMH weirdness along the way)

modules/pdp10/lib/defines.js

@@ -56,6 +56,11 @@ var APPNAME = "PDPjs";          // this @define is the default application name
  */
 var DEBUGGER = true;            // this @define is overridden by the Closure Compiler to remove Debugger-related support
 
+/*
+ * Set this to true to enable behavior compatible with SIMH.
+ */
+var SIMH = false;
+
 /*
  * Combine all the shared globals and machine-specific globals into one machine-specific global object,
  * which all machine components should start using; eg: "if (PDP10.DEBUG) ..." instead of "if (DEBUG) ...".