[Nauty] Old version string left in nauty.pc

[Michael Orlitzky]

A minor bug report: looking in the nauty.pc.in for 27r4, I have

  Version: 27r3

FWIW, I would suggest reusing the version passed to AC_INIT in
configure.ac by changing the above line to,

  Version: @PACKAGE_VERSION@

That way it never goes stale.

...and, a request: have you given any thought to a more common
versioning scheme, like 2.7.4 instead of 27r4 or 2.7r4? The current
format causes unnecessary stress. For example, the version number used
in the nauty.pc file above typically comes into play when another piece
of software wants to depend on a "new enough" version of nauty. It will
do this by executing,

  PKG_CHECK_MODULES([NAUTY], [nauty >= ???]

in its ./configure script. Problem is, PKG_CHECK_MODULES is expecting
to be able to look at the version in the installed nauty.pc file and
compare it to the version that the user wants. It knows that, say,
2.7.3 is older than 2.7.4 -- but it doesn't grok the "27r4" format,
somewhat defeating the purpose.

Distribution packagers (hi) have a similar problem when assigning
versions to their nauty packages. Package managers like apt and yum
understand 2.7.4, but not 27r4. As a result, we are all inventing our
own versioning schemes independently,

  https://repology.org/project/nauty/versions

leading to duplicated effort cross-distro issues.

Thanks for hearing me out =)