Merge pull request #1202 from mathics/notebooks

adding System`Noteboooks to the settings.m file

Author: rocky

CHANGES.rst

@@ -14,6 +14,7 @@ New builtins
 * ``FileNames``
 * ``NIntegrate``
 * ``PartitionsP``
+* ``$Notebooks``
 
 Enhancements
 ++++++++++++

mathics/autoload/settings.m

@@ -10,3 +10,9 @@
 Settings`$PreferredBackendMethod::usage = "Set this do whether to use mpmath, numpy or Sympy for numeric and symbolic constants and methods when there is s choice";
 Settings`$PreferredBackendMethod = "sympy"
 Unprotect[Settings`$PreferredBackendMethod]
+
+(* Some packages like Feyncalc, test for whether a they are being used
+inside a notbook. *)
+System`$Notebooks::usage = "Set True if the Mathics is being used with a notebook‐based front end.";
+System`$Notebooks = False;
+Unprotect[System`Notebooks];