mac: fix percent-encoding of non-utf-8 characters (issue4999)

help: support loading sub-topics If a sub-topic/section is requested and the main topic corresponds to a topic with sub-topics, we now look for and return content for a sub-topic if found. With this patch, `hg help internals.X` now works. hgweb does not yet render sub-topics, however.

help: pass sub-topic into help query functions While we will likely only use this variable in helptopic(), all these functions are called with the same arguments, so we have to be consistent.

help: pass subtopic into help() Now that we have multiple directories where help topics can live, we need a mechanism to access them. We already use "." to separate topic from section. So it seems logical to also use "." to denote the sub-directory of a topic. This patch teaches the help command to parse out the possible sub-topic and pass it to the help system.

help: add "internals" topic We introduce the "internals" help topic, which renders an index of available sub-topics. The sub-topics themselves are still not reachable via the help system.

help: teach loaddoc to load from a different directory The help system currently only supports showing help topics from a single directory. We'll need to teach it to show results from different directories in order to show the internals topics. The first step is to teach loaddoc() to load documentation from a sub-directory.

setup.py: package internals help files mpm says internal docs should be visible via `hg help` and hgweb. They need to be in the distribution for this to work. Package them.