check if file or path already exists, and append number "_(1)"
@param {String} filePath full path
@param {Boolean} isDir
@param {Function} callback
@param {Number} count
function checkExistsName(filePath, isDir, callback, count){ // callback(err, fullPath)
    if(typeof callback !== 'function') throw new Error('Wrong arguments');
    var pathInfo = resolve(filePath), newFullPath, oldName;
    count = count || 1;
    
    fs.exists(pathInfo.fullPath, function(exists){
        if(!exists) callback(null, pathInfo.fullPath);
        else { // generate new file or dir name, and try again
            oldName = count>1 ? '('+(count-1)+')' : '';
            if(isDir) {
                newFullPath = pathInfo.fullPath.replace(new RegExp(oldName.escape()+'$'),'') + '(' +count+ ')';
            }
            else {
                oldName = oldName + '.' + pathInfo.extName;
                newFullPath = pathInfo.fullPath.replace(new RegExp(oldName.escape()+'$'), '(' +count+ ').' + pathInfo.extName);
            }
            checkExistsName(newFullPath, isDir, callback, count+1);
        }
    });
}