While chasing down a possible HTTP/2 problem in our test suite (which
turns out not to be a Git bug, I think), I tried running the tests with
LIB_HTTPD_SSL=1, as TLS affects HTTP/2 upgrade.

Sadly, apache would not start at all with our ssl config. It looks like
this has probably been broken for many years, depending on your apache
and openssl versions.

The final two patches here fix ssl problems I found. The first two
patches drop support for older apache. This yields some minor cleanups,
and makes the ssl fixes slightly easier. I've cc'd Todd as the last
person to express support for Apache 2.2, in 2017. I'm hoping even
CentOS has moved on by now, but we'll see. :)

  [1/4]: t/lib-httpd: bump required apache version to 2.2
  [2/4]: t/lib-httpd: bump required apache version to 2.4
  [3/4]: t/lib-httpd: drop SSLMutex config
  [4/4]: t/lib-httpd: increase ssl key size to 2048 bits

 t/lib-httpd.sh          | 11 +++++++----
 t/lib-httpd/apache.conf | 31 ++++---------------------------
 t/lib-httpd/ssl.cnf     |  2 +-
 3 files changed, 12 insertions(+), 32 deletions(-)

-Peff