KHR_vulkan_glsl: name mangle distinguish pure textures.

Fixes issue #252.

Test/baseResults/vulkan.frag.out

@@ -31,7 +31,9 @@ ERROR: 0:66: 'non-opaque uniforms outside a block' : not allowed when using GLSL
 ERROR: 0:67: 'subroutine' : not allowed when generating SPIR-V 
 ERROR: 0:67: 'uniform' : no qualifiers allowed for function return 
 ERROR: 0:69: 'non-opaque uniforms outside a block' : not allowed when using GLSL for Vulkan 
-ERROR: 31 compilation errors.  No code generated.
+ERROR: 0:73: 'texture' : no matching overloaded function found 
+ERROR: 0:74: 'imageStore' : no matching overloaded function found 
+ERROR: 33 compilation errors.  No code generated.
 
 
 

Test/vulkan.frag

@@ -67,3 +67,9 @@ subroutine int fooS;                              // ERROR, not in SPV
 subroutine int fooSub();                          // ERROR, not in SPV
 
 uniform vec4 dv4;                                 // ERROR, no default uniforms
+
+void fooTex()
+{
+    texture(t2d, vec2(1.0));                 // ERROR, need a sampler, not a pure texture
+    imageStore(t2d, ivec2(4, 5), vec4(1.2)); // ERROR, need an image, not a pure texture
+}