Backport from https://trac.osgeo.org/grass/changeset/39475 in develbranch_6. Enhanced RunCommand to return returncode, stdout, and stderr.

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@39569 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gui_modules/gcmd.py

@@ -594,4 +594,7 @@ def RunCommand(prog, flags = "", overwrite = False, quiet = False, verbose = Fal
     if not getErrorMsg:
         return stdout
     
+    if read and getErrorMsg:
+        return ret, stdout, stderr
+    
     return stdout, stderr