GLSL: Fix #822: Improve information given for syntax errors.

Also, fixed one test file that didn't have its syntax error as the last line.

glslang/MachineIndependent/glslang.y

@@ -63,6 +63,8 @@ using namespace glslang;
 
 %}
 
+%define parse.error verbose
+
 %union {
     struct {
         glslang::TSourceLoc loc;