[meld] build_helpers: Fix environment variable silly

[Kai Willadsen <kaiw src gnome org>]

commit 4abf02c1612bb983a52c8d20112d96f23ca28d21
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sat Mar 8 09:54:04 2014 +1000

    build_helpers: Fix environment variable silly

 meld/build_helpers.py |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/meld/build_helpers.py b/meld/build_helpers.py
index 6474402..1eb74e0 100644
--- a/meld/build_helpers.py
+++ b/meld/build_helpers.py
@@ -291,7 +291,8 @@ class install_data(distutils.command.install_data.install_data):
     def finalize_options(self):
         distutils.command.install_data.install_data.finalize_options(self)
         if self.no_compile_schemas is None:
-            self.no_compile_schemas = bool(os.environ['NO_COMPILE_SCHEMAS'])
+            self.no_compile_schemas = bool(
+                os.environ.get('NO_COMPILE_SCHEMAS', None))
 
     def run(self):
         distutils.command.install_data.install_data.run(self)