platform.dist() returns ('debian', 'lenny/sid', '') on my Ubuntu 8.04
Hardy system.  Investigating shows that there are a few techniques in
platform.py to parse the version-number-files of different Linux
distributions.  This patch adds a command to try executing "lsb_release"
first of all.  lsb_release is the standard way to do this, originally
published in 2001:

http://refspecs.freestandards.org/LSB_1.0.0/gLSB/lsbrelease.html

and currently standardized here:

http://refspecs.freestandards.org/LSB_3.2.0/LSB-Core-generic/LSB-Core-generic/lsbrelease.html

If invoking "lsb_release" results in exit code 0 and some non-empty,
non-all-whitespace string on stdout, then dist() returns that.  Else,
dist falls back to the old (current) hacks.

There is a drawback to this: invoking three successive subprocesses
takes a bit of time.  Hopefully nobody needs to invoke platform.dist()
in a time-critical moment...

With this patch, platform.dist() return:
('Ubuntu', '8.04', 'hardy')

Oh, this patch also updates the docstring of dist() to explain what is
meant by "distribution", "version", and "id".