change isChannel pattern

#### Resolves #39 and #40


**Changes:**
```js
var isChannel = !!this._channelName;
if (isChannel) { ... }
_log.apply(this, [this._channelName, name].concat(args));
isChannel ? 'foo' + this._channelName + 'bar' : '';

// instead:
var channelName = this._channelName;
if (channelName) { ... }
_log.apply(this, [channelName, name].concat(args));
channelName ? 'foo' + channelName + 'bar' : '';

// minifies a lot better
var c=!!this._channelName;if(c){...}l.apply(this,[this._channelName,b].concat(a));c?'foo'+this._channelName+'bar':'';
var c=this._channelName;if(c){...}l.apply(this,[c,b].concat(a));c?'foo'+c+'bar':'';
```