Fix #6378. Start IDLE using the proper version of Python based on the directory

tree that idle.bat resides in.

Works with any/all versions of Python installed concurrently.

Lib/idlelib/idle.bat

 @echo off
-rem Working IDLE bat for Windows - uses start instead of absolute pathname
-start idle.pyw %1 %2 %3 %4 %5 %6 %7 %8 %9
+rem Start IDLE using the appropriate Python interpreter
+set CURRDIR=%~dp0
+start %CURRDIR%..\..\pythonw.exe %CURRDIR%idle.pyw %1 %2 %3 %4 %5 %6 %7 %8 %9

Misc/NEWS

@@ -32,6 +32,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #6378: idle.bat now runs with the appropriate Python version rather than
+  the system default. Patch by Sridhar Ratnakumar.
+
 - Issue #10470: 'python -m unittest' will now run test discovery by default,
   when no extra arguments have been provided.