Merge pull request #213 from nejstastnejsistene/master

aspen wrongfully catches IOErrors that occur within configuration scripts
Add Changelog for 0.25.3
Release 0.25.3
Bump version to 0.25.3-dev
add a test to verify that redirects don't add extra headers
Don't call error_late hooks on raised Response objects
Fix #165 - make explicit which vars are available to templates

As with python modules, if section 2 has an __all__ variable,
only the variables whose names are in that list are 'exported' to
the template.
test type returned not the returned value
Merge pull request #214 from gittip/issue165

Fix #165 - make explicit which vars are available to templates
update changelog
Fix #216 example that let a user astray.