Make sure spec documents #pragma once

Author: lgritz

src/doc/languagespec.tex

@@ -62,7 +62,7 @@
 \emph{lg@imageworks.com}
 }
 \date{{\large Date: 14 Jan, 2016 \\
- (with corrections, 30 Apr 2016)
+ (with corrections, 14 Jun 2016)
 }
 \bigskip
 \bigskip
@@ -854,6 +854,7 @@ \section{Preprocessor}
 \indexapi{\#else}
 \indexapi{\#endif}
 \indexapi{\#include}
+\indexapi{\#pragma}
 
 Shader source code is passed through a standard C preprocessor as a
 first step in parsing.  
@@ -876,6 +877,7 @@ \section{Preprocessor}
     #else
     #endif
     #include
+    #pragma once
 \end{code}