FilterLinesEnvironmentMixin.filter_body(): invoke superclass function.

FilterLinesEnvironmentMixin.filter_body() previously forgot to apply
the superclass version of the function before applying its own
transformation.
Do not repeat common part of environment in KNOWN_ENVIRONMENTS.

Set up the basic environment in choose_environment(), and only use
KNOWN_ENVIRONMENTS to choose between GenericEnvironmentMixin and
GitoliteEnvironmentMixin.
Add methods Environment.get_reply_to_refchange() and get_reply_to_commit().

Use these new methods instead of the old instance attributes
reply_to_refchange and reply_to_commit.
Pass ReferenceChange argument to Environment.get_reply_to_refchange().
Pass Revision argument to Environment.get_reply_to_commit().
Replace Revision.get_author() method with attribute.
Move the processing of special "reply to" values to the config environment.

Process the special values "pusher", "author", and "none" in
ConfigOptionsEnvironmentMixin rather than in the Change classes.
Merge branch 'environment-reply-to'

Make the Environment responsible for selecting the values for
"Reply-to" headers via new methods
Environment.get_reply_to_refchange() and get_reply_to_commit().