With version 1.50f19 the new feature was introduced.
I'm not able to use it as intended.

The minimal macro saved as New_ijm in two different directories (C:\Temp and the plugins folder of Fiji)
   requires("1.50f");
   var name = getInfo("macro.filepath");
   IJ.log(name);
always returns the pat to AutoRun_Scripts.ijm (e.g. H:\Fiji.app\/macros/AutoRun/AutoRun_Scripts.ijm).
The same result is given when using Macro_Runner.getFilePath() in a Jython script.
   from ij import IJ
   from ij.plugin import Macro_Runner
   name = Macro_Runner.getFilePath()
   IJ.log(name)

I have tested both (macro and script) with the ImageJ development snapshot updated to 1.50f19, where the macro returns 'null' and the script returns nothing (log does not show up).

Information about your version of Java:

  os.arch => amd64
  os.name => Windows 7
  os.version => 6.1
  java.version => 1.6.0_24
  java.vendor => Sun Microsystems Inc.
  java.runtime.name => Java(TM) SE Runtime Environment
  java.runtime.version => 1.6.0_24-b07
  java.vm.name => Java HotSpot(TM) 64-Bit Server VM
  java.vm.version => 19.1-b02
  java.vm.vendor => Sun Microsystems Inc.
  java.vm.info => mixed mode
  java.awt.graphicsenv => sun.awt.Win32GraphicsEnvironment
  java.specification.name => Java Platform API Specification
  java.specification.version => 1.6
  sun.cpu.endian => little
  sun.desktop => windows
  file.separator => \

The up-to-date check says: REMIND_LATER

Information relevant to JAVA_HOME related problems:

  JAVA_HOME is set to: H:\Fiji.app/java/win64/jdk1.6.0_24//jre
  imagej.dir => H:\Fiji.app

Information about the version of each plugin:

Activated update sites:
ImageJ: http://update.imagej.net/ (last check:20151221201554)
Fiji: http://update.fiji.sc/ (last check:20151221100640)

Files not up-to-date:
  e7c170f1 (MODIFIED) 20151222104614 jars/ij-1.50e.jar
  c4cc215d (LOCAL_ONLY) 20151222110049 plugins/New_.ijm