[issue1543] Improve hg serve to make testing easier

[Marcus Lindblom]

New submission from Marcus Lindblom <macke at yar.nu>:

The Mercurial tests for BuildBot are a bit more complicated than necessary due
to two facts:
 1. Output isn't flushed, so we can't know when it's up and running (i.e. read
'Listening to port xxxx....')
 2. Not being able to pick a free random port, using --port=0 (or something), so
we have to choose one and hope that it's free. (currently using 8300 + getpid()
% 300)

This makes it easier to programmatically launch hg serve and interact with it in
BuildBot's unit tests.

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messages: 8770
nosy: marcusl
priority: wish
status: unread
title: Improve hg serve to make testing easier

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Mercurial issue tracker <mercurial-bugs at selenic.com>
<http://www.selenic.com/mercurial/bts/issue1543>
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