[gegl] operations: Use the double version of abs in image-compare

[Téo Mazars <teom src gnome org>]

commit 4e0eecd3d3f3ae653c6b66ec48d24acb560a0842
Author: Téo Mazars <teo mazars ensimag fr>
Date:   Wed Oct 16 11:19:26 2013 +0200

    operations: Use the double version of abs in image-compare
    
    ... instead of the integer version.

 operations/common/image-compare.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/operations/common/image-compare.c b/operations/common/image-compare.c
index c2862a4..93b2a6c 100644
--- a/operations/common/image-compare.c
+++ b/operations/common/image-compare.c
@@ -118,7 +118,7 @@ process (GeglOperation       *operation,
                                SQR (data_in1[1] - data_in2[1]) +
                                SQR (data_in1[2] - data_in2[2]));
 
-          gdouble alpha_diff = abs (data_in1[3] - data_in2[3]) * 100.0;
+          gdouble alpha_diff = fabs (data_in1[3] - data_in2[3]) * 100.0;
 
           diff = MAX (diff, alpha_diff);