src/sage/functions/piecewise.py: needs sage.libs.giac -> needs giac

Some tests in this file use the giac pexpect interface but are tagged
with "needs sage.libs.giac". Now that we have a feature for the giac
executable, "needs giac" is more appropriate.

Author: orlitzky

src/sage/functions/piecewise.py

@@ -1470,16 +1470,18 @@ def _giac_init_(self, parameters, variable):
 
             EXAMPLES::
 
+                sage: # needs giac
                 sage: ex = piecewise([((0, 1), pi), ([1, 2], x)])
-                sage: f = ex._giac_(); f                                                # needs sage.libs.giac
+                sage: f = ex._giac_(); f
                 piecewise(((sageVARx>0) and (1>sageVARx)),pi,((sageVARx>=1) and (2>=sageVARx)),sageVARx)
-                sage: f.diff(x)                                                         # needs sage.libs.giac
+                sage: f.diff(x)
                 piecewise(((sageVARx>0) and (1>sageVARx)),0,((sageVARx>=1) and (2>=sageVARx)),1)
 
-                sage: ex = piecewise([((-100, -2), 1/x), ((1, +oo), cos(x))])           # needs sage.libs.giac
-                sage: g = ex._giac_(); g                                                # needs sage.libs.giac
+                sage: # needs giac
+                sage: ex = piecewise([((-100, -2), 1/x), ((1, +oo), cos(x))])
+                sage: g = ex._giac_(); g
                 piecewise(((sageVARx>-100) and ((-2)>sageVARx)),1/sageVARx,sageVARx>1,cos(sageVARx))
-                sage: g.diff(x)                                                         # needs sage.libs.giac
+                sage: g.diff(x)
                 piecewise(((sageVARx>-100) and ((-2)>sageVARx)),-1/sageVARx^2,sageVARx>1,-sin(sageVARx))
 
             TESTS::