[gimp] app: add "#include <gegl.h>" to tests

[N/A <ell src gnome org>]

commit fdd8b3f4f6c7b68c979df8b36c43b0130066a2b8
Author: Ell <ell_se yahoo com>
Date:   Sat Oct 28 10:52:54 2017 -0400

    app: add "#include <gegl.h>" to tests
    
    Needed since commit c5b88702e6a9abbdb9bf93f1859ae65ac7acc3b2.

 app/tests/test-session-2-6-compatibility.c         |    1 +
 .../test-session-2-8-compatibility-multi-window.c  |    1 +
 .../test-session-2-8-compatibility-single-window.c |    1 +
 3 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/app/tests/test-session-2-6-compatibility.c b/app/tests/test-session-2-6-compatibility.c
index 0333655..50d611e 100644
--- a/app/tests/test-session-2-6-compatibility.c
+++ b/app/tests/test-session-2-6-compatibility.c
@@ -17,6 +17,7 @@
 
 #include "config.h"
 
+#include <gegl.h>
 #include <gtk/gtk.h>
 
 #include "dialogs/dialogs-types.h"
diff --git a/app/tests/test-session-2-8-compatibility-multi-window.c 
b/app/tests/test-session-2-8-compatibility-multi-window.c
index c46341f..165943d 100644
--- a/app/tests/test-session-2-8-compatibility-multi-window.c
+++ b/app/tests/test-session-2-8-compatibility-multi-window.c
@@ -17,6 +17,7 @@
 
 #include "config.h"
 
+#include <gegl.h>
 #include <gtk/gtk.h>
 
 #include "dialogs/dialogs-types.h"
diff --git a/app/tests/test-session-2-8-compatibility-single-window.c 
b/app/tests/test-session-2-8-compatibility-single-window.c
index 3f56644..78a6a04 100644
--- a/app/tests/test-session-2-8-compatibility-single-window.c
+++ b/app/tests/test-session-2-8-compatibility-single-window.c
@@ -17,6 +17,7 @@
 
 #include "config.h"
 
+#include <gegl.h>
 #include <gtk/gtk.h>
 
 #include "dialogs/dialogs-types.h"