Add new API linux_distribution() which supports reading the full distribution
name and also knows how to parse LSB-style release files.

Redirect the old dist() API to the new API (using the short distribution name
taken from the release file filename).

Add branch and revision to _sys_version().

Add work-around for Cygwin to libc_ver().

Add support for IronPython (thanks for Anthony Baxter) and make
Jython support more robust.