Fix bug in function name comparison.

AbstractFunctionRestrictionsSniff did not allow for case-insensitive comparison of function names.

> **Note**: Function names are case-insensitive, though it is usually good form to call functions as they appear in their declaration.

Ref: http://php.net/manual/en/functions.user-defined.php

Also:
* Better be safe than sorry, so `preg_quote()`-ing the function names passed to this class.
* Minor memory management improvement: no need to remember the matched function name.

WordPress/AbstractFunctionRestrictionsSniff.php

@@ -105,10 +105,10 @@ public function process( PHP_CodeSniffer_File $phpcsFile, $stackPtr ) {
 				continue;
 			}
 
-			$functions = implode( '|', $group['functions'] );
-			$functions = preg_replace( '#[^\.]\*#', '.*', $functions ); // So you can use * instead of .*
+			$functions = array_map( array( $this, 'prepare_functionname_for_regex' ), $group['functions'] );
+			$functions = implode( '|', $functions );
 
-			if ( preg_match( '#\b(' . $functions . ')\b#', $token['content'] ) < 1 ) {
+			if ( preg_match( '`\b(?:' . $functions . ')\b`i', $token['content'] ) < 1 ) {
 				continue;
 			}
 
@@ -130,4 +130,22 @@ public function process( PHP_CodeSniffer_File $phpcsFile, $stackPtr ) {
 
 	} // end process()
 
+	/**
+	 * Prepare the function name for use in a regular expression.
+	 *
+	 * The getGroups() method allows for providing function with a wildcard * to target
+	 * a group of functions. This prepare routine takes that into account while still safely
+	 * escaping the function name for use in a regular expression.
+	 *
+	 * @param string $function Function name.
+	 * @return string Regex escaped lowercase function name.
+	 */
+	protected function prepare_functionname_for_regex( $function ) {
+		$function = str_replace( array( '.*', '*' ) , '#', $function ); // Replace wildcards with placeholder.
+		$function = preg_quote( $function, '`' );
+		$function = str_replace( '#', '.*', $function ); // Replace placeholder with regex wildcard.
+
+		return $function;
+	}
+
 } // end class