Use #version 140 to get inverse()

The Linux GLSL imlementation is very loose in its interpretation of
standards, it seems. (I am not surprised.) Not so on Windows, at least
with AMD drivers. The inverse() function (for float matririces) is
present only starting from GLSL 1.40. Bump the #version directive
accordingly. (See
https://www.opengl.org/sdk/docs/man/html/inverse.xhtml)

To get this to work again on OS X will be a further challenge. There a
'legacy' context only has GLSL 1.20. But the intent is to move this
code in the direction of using 'core' contexts anyway.

Change-Id: I572dc7cc30f90321b233fbfd857455dc01761a7c

slideshow/opengl/basicVertexShader.glsl

@@ -26,7 +26,7 @@
  *
  ************************************************************************/
 
-#version 120
+#version 140
 
 attribute vec3 a_position;
 attribute vec3 a_normal;

slideshow/opengl/glitterVertexShader.glsl

@@ -7,7 +7,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-#version 130
+#version 140
 
 #define M_PI 3.1415926535897932384626433832795
 

slideshow/opengl/reflectionVertexShader.glsl

@@ -26,7 +26,7 @@
  *
  ************************************************************************/
 
-#version 130
+#version 140
 
 attribute vec3 a_position;
 attribute vec3 a_normal;

slideshow/opengl/vortexVertexShader.glsl

@@ -7,7 +7,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-#version 120
+#version 140
 
 #define M_PI 3.1415926535897932384626433832795