using color-tests backwards-portably

[Jim Meyering]

Hi Ralf,

I'd like to use automake-1.11's color-tests option
in libguestfs -- and more importantly, parallel-tests,
but we may have a build-from-clone requirement on
systems with automake older than 1.11.
On those systems, it's fine to ignore or disable these
two unsupported options.

I proposed a configure.ac-modifying "solution",

    https://www.redhat.com/archives/libguestfs/2009-August/msg00160.html

but it's too ugly.

Can you think of another way?

[I know I could roll my own via check.mk, like what coreutils
used prior to automake-1.11, but would rather use automake's own
support for those options, when possible. ]

Thanks,

Jim