src/sage/interfaces/maxima_abstract.py: use maxima_calculus in a doctest

It probably doesn't matter, but we should prefer the maxima library
interface anywhere that performance might be an issue. We now test
the _commands() method with maxima_calculus (a library interface)
rather than "maxima" (a pexpect interface).

Author: orlitzky

src/sage/interfaces/maxima_abstract.py

@@ -307,7 +307,7 @@ def _commands(self):
         Maxima), so we look only for a few reliable commands::
 
             sage: # long time
-            sage: cs = maxima._commands()
+            sage: cs = maxima_calculus._commands()
             sage: "display" in cs
             True
             sage: "gcd" in cs