glsl_symbol_table: Add new talloc-based new()

We take advantage of overloading of the new operator (with an
additional parameter!) to make this look as "C++ like" as possible.

This closes 507 memory leaks when compiling glsl-orangebook-ch06-bump.frag
when measured with:

	valgrind ./glsl glsl-orangebook-ch06-bump.frag

as seen here:

	total heap usage: 55,623 allocs, 14,389 frees
	(was 13,882 frees before)

1 files changed, 33 insertions, 0 deletions

diff --git a/glsl_symbol_table.h b/glsl_symbol_table.h
index 26b90fdb7c..ae2fd3f4f1 100644
--- a/glsl_symbol_table.h
+++ b/glsl_symbol_table.h
@@ -26,6 +26,8 @@
 #ifndef GLSL_SYMBOL_TABLE
 #define GLSL_SYMBOL_TABLE
 
+#include <new>
+
 #include "symbol_table.h"
 #include "ir.h"
 #include "glsl_types.h"
@@ -44,7 +46,38 @@ private:
       glsl_function_name_space = 2
    };
 
+   static int
+   _glsl_symbol_table_destructor (glsl_symbol_table *table)
+   {
+      table->~glsl_symbol_table();
+
+      return 0;
+   }
+
 public:
+   /* Callers of this talloc-based new need not call delete. It's
+    * easier to just talloc_free 'ctx' (or any of its ancestors). */
+   static void* operator new(size_t size, void *ctx)
+   {
+      void *table;
+
+      table = talloc_size(ctx, size);
+      assert(table != NULL);
+
+      talloc_set_destructor(table, (int (*)(void*)) _glsl_symbol_table_destructor);
+
+      return table;
+   }
+
+   /* If the user *does* call delete, that's OK, we will just
+    * talloc_free in that case. Here, C++ will have already called the
+    * destructor so tell talloc not to do that again. */
+   static void operator delete(void *table)
+   {
+      talloc_set_destructor(table, NULL);
+      talloc_free(table);
+   }
+   
    glsl_symbol_table()
    {
       table = _mesa_symbol_table_ctor();