Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Lib/plat-mac/buildtools.py b/Lib/plat-mac/buildtools.py
index bebab19..365772a 100644
--- a/Lib/plat-mac/buildtools.py
+++ b/Lib/plat-mac/buildtools.py
@@ -55,7 +55,7 @@
         except (Carbon.File.Error, ValueError):
             continue
     else:
-        raise BuildError, "Template %s not found on sys.path" % `template`
+        raise BuildError, "Template %r not found on sys.path" % (template,)
     file = file.as_pathname()
     return file