Experimental lexer generator: fix build after jinja2 came along.

tools/lexer_generator/code_generator.py

Index: tools/lexer_generator/code_generator.py
diff --git a/tools/lexer_generator/code_generator.py b/tools/lexer_generator/code_generator.py
index 34f6f5ffa733fb179814b8dd71ae77b7c9a24021..4c6b033540b8425a50c56697c6ccaffb0a10a866 100644
--- a/tools/lexer_generator/code_generator.py
+++ b/tools/lexer_generator/code_generator.py
@@ -27,6 +27,8 @@
 
 from dfa import Dfa
 import jinja2
+import os
+import sys
 
 class CodeGenerator:
 
@@ -50,6 +52,7 @@ class CodeGenerator:
     assert(default_action and default_action.match_action())
     default_action = default_action.match_action()
 
+    sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
     template_env = jinja2.Environment(
       loader = jinja2.PackageLoader('lexer_generator', '.'),
       undefined = jinja2.StrictUndefined)