Fix for issue #2573: Can't change the framework name on OS X builds

This introduces a new configure option: --with-framework-name=NAME
(defaulting to 'Python'). This allows you to install several copies
of the Python framework with different names (such as a normal build
and a debug build).
diff --git a/Mac/BuildScript/build-installer.py b/Mac/BuildScript/build-installer.py
index 37974e9..1fd2439 100755
--- a/Mac/BuildScript/build-installer.py
+++ b/Mac/BuildScript/build-installer.py
@@ -199,7 +199,7 @@
     dict(
         name="PythonApplications",
         long_name="GUI Applications",
-        source="/Applications/MacPython %(VER)s",
+        source="/Applications/Python %(VER)s",
         readme="""\
             This package installs IDLE (an interactive Python IDE),
             Python Launcher and Build Applet (create application bundles