OpenVPN Release 2.7_beta2

OpenVPN Release 2.7_beta2

version.m4, ChangeLog, Changes.rst

Changes.rst has not received an "2.7_beta2" 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 beta1 -> beta2 are:
   - even more of signed/unsigned related warnings have been fixed
   - #pragmas have been added to all to-be-fixed source files, so we can
     now always enable -Wconversion to see if new code brings new warnings
     (and the CI infra builds with -Werror)
   - add proper input sanitation to DNS strings to prevent an attack
     coming from a trusted-but-malicous OpenVPN server (CVE: 2025-10680,
     affects unixoid systems with --dns-updown scripts and windows using
     the built-in powershell call)
   - greatly improved event log handling for the Windows interactive service
     - this brings build system changes and a new openvpnservmsg.dll
   - bugfixes when using multi-socket on windows
     (properly recognize that TCP server mode does not work with DCO,
     properly handle TCP multi-socket server setups without DCO)
   - bring back configuring of IPv4 broadcast addresses on Linux
     (also backported to 2.6.15)
   - Rename Fox Crypto to Sentyron in copyright notices
   - Switch test_ssl certificate from RSA 2048 to secp384r1
     (so "make check" runs with OpenSSL set to @SECLEVEL=3)
   - repair "--dhcp-option DNS" setting in combination with DHCP (TAP)
     or --up scripts (GH issue #839, #840)
   - clean up MI prefix handling
   - replace all assert() calls with OpenVPN ASSERT()