_cairo_pattern_get_extents: Fix to allow for expansion based on filter

This fixes the filter-bilinear-extents test case and the
related bug entry:

	bad clipping with EXTEND_NONE
	http://bugs.freedesktop.org/show_bug.cgi?id=15349

Though there are still differences in the PDF and PostScript
backends, (primarily because we can't capture cairo's filter
modes in those file formats).

src/cairo-pattern.c

@@ -2098,6 +2098,28 @@ _cairo_pattern_get_extents (cairo_pattern_t         *pattern,
 	x2 = x1 + surface_extents.width;
 	y2 = y1 + surface_extents.height;
 
+	/* The filter can effectively enlarge the extents of the
+	 * pattern, so extend as necessary. Note: We aren't doing any
+	 * backend-specific querying of filter box sizes at this time,
+	 * (since currently no specific backends that could do custom
+	 * filters are calling _cairo_pattern_get_extents). */
+	switch (pattern->filter) {
+	case CAIRO_FILTER_GOOD:
+	case CAIRO_FILTER_BEST:
+	case CAIRO_FILTER_BILINEAR:
+	    x1 -= 0.5;
+	    y1 -= 0.5;
+	    x2 += 0.5;
+	    y2 += 0.5;
+	    break;
+	case CAIRO_FILTER_FAST:
+	case CAIRO_FILTER_NEAREST:
+	case CAIRO_FILTER_GAUSSIAN:
+	default:
+	    /* Nothing to do */
+	    break;
+	}
+
 	imatrix = pattern->matrix;
 	status = cairo_matrix_invert (&imatrix);
 	/* cairo_pattern_set_matrix ensures the matrix is invertible */