Update libevent 2.1.8 stable for 123.09beta01

- Update libevent from 2.0.22 stable to 2.1.8 which includes OpenSSL fixes and OpenSSL 1.1 compatibility support and security fixes https://github.com/libevent/libevent/blob/release-2.1.8-stable/ChangeLog. Centmin Mod's usage of libevent is specifically for custom compiled Memcached server which is compiled against libevent 2.1.8 instead of 2.0.22 now.
- For existing users, updating Centmin Mod 123.09beta01 via centmin.sh menu option 23 submenu option 2, then exiting centmin.sh and re-running centmin.sh menu option 10 will recompile Memcached server against updated libevent 2.1.8 version release.

centmin.sh

@@ -555,7 +555,7 @@ IMAGICKPHP_VER='3.4.3'   # PHP extension for imagick
 MAILPARSEPHP_VER='2.1.6'    # https://pecl.php.net/package/mailparse
 MAILPARSEPHP_COMPATVER='3.0.1' # For PHP 7
 MEMCACHED_INSTALL='y'         # Install Memcached
-LIBEVENT_VERSION='2.0.22'   # Use this version of Libevent
+LIBEVENT_VERSION='2.1.8'   # Use this version of Libevent
 MEMCACHED_VERSION='1.4.36'  # Use this version of Memcached server
 MEMCACHE_VERSION='3.0.8'    # Use this version of Memcache
 MEMCACHEDPHP_VER='2.2.0'    # Memcached PHP extension not server

example/custom_config.inc

@@ -237,7 +237,7 @@ IMAGICKPHP_VER='3.4.3'   # PHP extension for imagick
 MAILPARSEPHP_VER='2.1.6'    # https://pecl.php.net/package/mailparse
 MAILPARSEPHP_COMPATVER='3.0.1' # For PHP 7
 MEMCACHED_INSTALL='y'       # Install Memcached
-LIBEVENT_VERSION='2.0.22'   # Use this version of Libevent
+LIBEVENT_VERSION='2.1.8'   # Use this version of Libevent
 MEMCACHED_VERSION='1.4.36'  # Use this version of Memcached server
 MEMCACHE_VERSION='3.0.8'    # Use this version of Memcache
 MEMCACHEDPHP_VER='2.2.0'    # Memcached PHP extension not server