Coding Standards: Fix instances of WordPress.PHP.NoSilencedErrors.Discouraged.

Noteable changes:
- The `magic_quotes_runtime` and `magic_quotes_sybase` settings were removed in PHP 5.4, so no longer need to be set.
- Some functions that use external libraries can generate errors that can't be tested for, so are globally allowed to silence errors.
- Quite a few functions would cause errors if `safe_mode` was set. This setting was removed in PHP 5.4.
- Only a handful of `header()` calls needed corresponding `headers_sent()` checks for unit tests to pass, but more may need to be added as the nightlies builds are tested.

See #46732.

Built from https://develop.svn.wordpress.org/trunk@45611


git-svn-id: http://core.svn.wordpress.org/trunk@45422 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/plugins.php

@@ -170,7 +170,7 @@ if ( $action ) {
 				error_reporting( E_CORE_ERROR | E_CORE_WARNING | E_COMPILE_ERROR | E_ERROR | E_WARNING | E_PARSE | E_USER_ERROR | E_USER_WARNING | E_RECOVERABLE_ERROR );
 			}
 
-			@ini_set( 'display_errors', true ); //Ensure that Fatal errors are displayed.
+			ini_set( 'display_errors', true ); //Ensure that Fatal errors are displayed.
 			// Go back to "sandbox" scope so we get the same errors as before
 			plugin_sandbox_scrape( $plugin );
 			/** This action is documented in wp-admin/includes/plugin.php */