Added extensible prompt facility to io.sys and wrote a small unit test
Added extensible request and response for context managers
Applied some pep8 spaces which were lacking
changed request_prompts to prompt_responses
merged the changes of @owenn into the new master branch and the a few changes to make it nicer
env can be accessed directly - no param needed
use 'prompts' instead of 'prompt_responses', seems to be the better shorter name
cleaned up tests, removed unnecessary _AliasDict, pep8
add prompts change to changelog
prompts documentation in usage/env.rst
python 2.5 needs future import for with statement
another small py2.5 glitch
Merge branch 'master' into 1021-int

Conflicts:
	docs/changelog.rst
Update changelog language + link to docs

Re #1021
Fix typo + language tweaks in 'prompts' docs.

Re #1021
Minor stylistic update re: dict iteration

Re #1021