Fixed heavy cpu usage in getBitmapWithFilterApplied

In case of a large image, IntBuffer's get/put uses too many CPU resources as a whole.
Please merge the branch to fix it.

#### Code to Reproduce
```java
GPUImage image = new GPUImage(this);
Bitmap srcBitmap = BitmapFactory.decodeResource(getResources(), R.raw.sample); // LARGE IMAGE!
image.setImage(srcBitmap);
image.setFilter(new GPUImageSepiaFilter());

Bitmap dstBitmap = image.getBitmapWithFilterApplied(); // HEAVY!
```
A simple activty to reproduce this problem is [here](https://github.com/amachang/android-gpuimage-sandbox/blob/master/src/jp/amachang/gpuimagesandbox/MainActivity.java#L31).


#### Profiling results (before fixing)
![before](https://raw.github.com/amachang/android-gpuimage-sandbox/master/tmp/before.png)


#### Profiling results (fixed)
![after](https://raw.github.com/amachang/android-gpuimage-sandbox/master/tmp/after.png)