make giac doctesting/feature optional

Author: dimpase

src/sage/features/giac.py

@@ -24,7 +24,7 @@ def __init__(self):
             True
         """
         Executable.__init__(self, 'giac', executable='giac',
-                            spkg='giac', type='standard')
+                            spkg='giac', type='optional')
 
 def all_features():
     return [Giac()]

src/sage/interfaces/giac.py

@@ -1,3 +1,4 @@
+# sage.doctest: optional - giac
 r"""
 Pexpect Interface to Giac