function exists( path, clbk ) {
	fcn( path, done );

	/**
	* Callback invoked upon performing a filesystem call.
	*
	* @private
	* @param {(Error|null)} error - error object
	* @returns {void}
	*/
	function done( error ) {
		if ( clbk.length === 2 ) {
			if ( error ) {
				return clbk( error, false );
			}
			return clbk( null, true );
		}
		if ( error ) {
			return clbk( false );
		}
		return clbk( true );
	}
}
Tests whether a path exists on the filesystem.

@param {(string|Buffer)} path - path to test
@param {Function} clbk - callback to invoke after testing path existence

@example
exists( __dirname, done );

function done( error, bool ) {
    if ( error ) {
        console.error( error );
    }
    if ( bool ) {
        console.log( '...path exists.' );
    } else {
        console.log( '...path does not exist.' );
    }
}