Bugfix ofImageTypeFromPixelFormat()& swapRgb()

[yty]

If not repaired, will not achieve the following example:

ofImage img;
ofImage imgEx;

//--------------------------------------------------------------
void ofApp::setup(){

    ofSetDataPathRoot("E:/GitHubFiles/openFrameworks/examples/graphics/imageLoaderExample/bin/data/images/");

    img.loadImage("transparency.png");
}

//--------------------------------------------------------------
void ofApp::update(){
    imgEx.setFromPixels(img.getPixelsRef(),img.width,img.height,OF_IMAGE_COLOR_ALPHA,ofGetMousePressed()); 
}

//--------------------------------------------------------------
void ofApp::draw(){
    img.draw(0,0);
    imgEx.draw(0,img.getHeight());
}

[kylemcdonald]

same issue here, we would like to merge 9d8d8e5 but the other commits make this a bit complicated. please re-submit with only 9d8d8e5 on top of openframeworks/master

[bilderbuchi]

also, please follow the guidelines in the contribution document, i.e. prepare a separate branch for each PR, then issues such as this can be more easily avoided. :-)