One-file `hg` executables and hosting solutions

[Matt Harbison]

I was looking at SCM Manager (which we use internally for hosting),
and stumbled across a thread where people were struggling with it on
Windows because the files don't exist in the filesystem with the
official release (py2exe puts them in library.zip). It *does* work for
the 5.6 release, where everything is in the filesystem for now.

They have a py file[1] that imports some hg code and then calls
`wsgicgi.launch(application)`, which is why there's a dependency on
having python installed and having access to Mercurial *.py files.
But this seems like it is similar to the issues with external python
code in the test suite that we discussed Sunday, and therefore we
could solve it without them needing an external python?  But IDK how
wsgicgi stuff works.

The comment about implementing the Mercurial protocol in an
extension[2] in the thread concerned me (because my mind went to the
wire protocol).  Is there some guidance we can provide them?

[1] https://github.com/scm-manager/scm-manager/blob/develop/scm-plugins/scm-hg-plugin/src/main/resources/sonia/scm/python/hgweb.py
[2] https://groups.google.com/d/msg/scmmanager/UNOdUCLCnz0/suWk136FAQAJ