output endpoint gradient for some angle tabulations

unittest/force-styles/tests/angle_table.txt

@@ -1,7 +1,7 @@
 # generated by gen_angle.py
 
 harmonic_1
-N 73 EQ 110.1
+N 73 FP 0.0456926 0.0456926 EQ 110.1
 
 1 0 276.943155662151 5.03075668777749
 2 2.5 264.509053358232 4.91652515535748
@@ -78,7 +78,7 @@ N 73 EQ 110.1
 73 180 111.627281943904 -3.19391364646364
 
 harmonic_2
-N 73 EQ 111
+N 73 FP 0.0274156 0.0274156 EQ 111
 
 1 0 168.893605313642 3.04312802366922
 2 2.5 161.371458903784 2.97458910421721

unittest/force-styles/tests/gen_angle_table.py

@@ -16,7 +16,11 @@ fac = 180.0/num
 
 for i in [1,2,3,4]:
     fp.write("\nharmonic_%d\n" % i)
-    fp.write("N %d EQ %g\n\n" % (num+1,theta0[i]))
+    if i > 2:
+      fp.write("N %d EQ %g\n\n" % (num+1,theta0[i]))
+    else:
+      grad=2.0*k[i]*M_PI/180.0*M_PI/180.0
+      fp.write("N %d FP %g %g EQ %g\n\n" % (num+1,grad, grad, theta0[i]))
 
     for j in range(num+1):
         theta = fac*j