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
Handle connection failures due to server load

SSHException with "Error reading SSH protocol banner" is raised when
sshd is unresponsive but Fabric treats it as an auth failure. This patch
fixes this by treating it as NetworkError.
Add a changelog entry for #948
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
Apply @akidata's fix re #965 + changelog
Merge branch '1.8' into 948-int

Conflicts:
	docs/changelog.rst
Merge branch '1.8'

Conflicts:
	docs/changelog.rst
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