Fix all PHP 8.1 test failures

* `strftime()` has been replaced with a polyfill based on `DateTime`.
* Explicit type casts/assertions added where required by PHP 8.1
* `filter_var(…, FILTER_SANITIZE_STRING)` replaced with `strip_tags()`
  or HTML entity encoding of quotation marks, depending on a guess of
  what the intended "sanitization" was
* `http_build_query()` usage type mismatches fixed
* Removed usages of the `FILE_TEXT` constant
* To avoid breaking PHP 5.6 compatibility (function return types),
  `e_session_db` no longer implements `SessionHandlerInterface`.
  Instead, the alternative non-OOP invocation of
  `session_set_save_handler()` is used instead to apply the session
  handler.
* The shim for `strptime()` still calls the native function if available
  but now suppresses the deprecation warning.

* `e_db_pdo` explicitly asks for `PDO::ATTR_STRINGIFY_FETCHES` to
  maintain consistent behavior with past versions of PHP.
* `e_db_mysql` explicitly sets `mysqli_report(MYSQLI_REPORT_OFF)` to
  maintain consistent behavior with past versions of PHP.

* Removed pointless random number generator seed from `banner` plugin
* Workaround for `COUNT(*)` SQL query in
  `validatorClass::dbValidateArray()` without a proper API for avoiding
  SQL injection

e107_handlers/session_handler.php

@@ -397,6 +397,7 @@ class e_session
 		if($key == null) // clear all under this namespace.
 		{
 			$this->_data = array(); // must be set to array() not unset.
+			return $this;
 		}
 
 		if(strpos($key,'/') !== false) // multi-dimensional
@@ -538,7 +539,14 @@ class e_session
 			//	ini_set('session.save_handler', 'user');
 
 				$session = new e_session_db;
-				session_set_save_handler($session, true);
+				session_set_save_handler(
+					[$session, 'open'],
+					[$session, 'close'],
+					[$session, 'read'],
+					[$session, 'write'],
+					[$session, 'destroy'],
+					[$session, 'gc']
+				);
 				$session->setSaveHandler();
 			break;
 
@@ -1112,7 +1120,12 @@ class e_core_session extends e_session
 }
 
 
-class e_session_db implements SessionHandlerInterface
+/**
+ * Database session handler
+ *
+ * @todo PHP 8.1 support with {@see SessionHandlerInterface}
+ */
+class e_session_db #implements SessionHandlerInterface
 {
 	/**
 	 * @var e_db