OpenVPN Release 2.7_rc1

OpenVPN Release 2.7_rc1

version.m4, ChangeLog, Changes.rst

Changes.rst has not received an "2.7_rc1" section - it has the
"highlevel" overview of what is new in 2.7, but for alpha/beta releases
it's better to look at git log to see what has been added/fixed.

Notable changes beta3 -> rc1 are:
    - even more type conversion related warnings have been fixed
    - more bugfixes related to BYTECOUNT display on the management
      interface and byte counters on DCO platforms in general
    - numerous minibugs reported by ZeroPath AI have been fixed
      (small memleaks, possible file descriptor leaks, improved
      sanity checks, add ASSERT() on function contracts, etc.)
    - add warning for unsupported combination of --push and --tls-server
    - add warning for unsupported combination of --reneg-bytes or
      --reneg-pkts with DCO
    - remove perf_push()/perf_pop() infrastructure (because it did not
      work anymore, and compiler profiling will give better results today)
    - ensure compatibility with OpenSSL 3.6.0 - specifically, do not crash
      in t_lpback.sh trying to use new encrypt-then-mac (ETM) ciphers
    - improved PUSH_UPDATE server side support, which now handles changes
      of pushed ifconfig/ifconfig-ipv6 addresses correctly (send packets
      to new IP addresses to this client, stop sending packets to the old
      addresses).
    - improve CONTRIBUTING documentation
    - add unit test for DHCP packet infrastructure
    - freshen URLs all over the tree, and change to HTTPS where possible
    - on DCO Linux/FreeBSD, add support for clients receiving an IPv4/IPv6
      address that is not part of the --server/--server-ipv6 subnet
      (= install extra on-interface host routes).
    - Windows programs use a new API for path name canonicalization now
      (PathCchCanonicalizeEx()) which will break building with MinGW on
      Ubuntu 22.04 -> Upgrade to 24.04 to make builds work again.
    - on Windows, when setting up WINS servers using netsh, use interface
      index instead of adapter name now ("as for all other netsh calls")
    - remove undocumented and unused --memstats feature

Signed-off-by: Gert Doering <gert@greenie.muc.de>