t/lib-httpd: bump required apache version to 2.2

t/lib-httpd: bump required apache version to 2.2

Apache 2.2 was released in 2005, almost 18 years ago. We can probably
assume that people are running a version at least that old (and the
stakes for removing it are fairly low, as the worst case is that they
would not run the http tests against their ancient version).

Dropping support for the older versions cleans up the config file a
little, and will also enable us to bump the required version further
(with more cleanups) in a future patch.

Note that the file actually checks for version 2.1. In apache's
versioning scheme, odd numbered versions are for development and even
numbers are for stable releases. So 2.1 and 2.2 are effectively the same
from our perspective.

Older versions would just fail to start, which would generally cause us
to skip the tests. However, we do have version detection code in
lib-httpd.sh which produces a nicer error message, so let's update that,
too. I didn't bother handling the case of "3.0", etc. Apache has been on
2.x for 21 years, with no signs of bumping the major version.  And if
they eventually do, I suspect there will be enough breaking changes that
we'd need to update more than just the numeric version check. We can
worry about that hypothetical when it happens.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>