apply EXIF rotation information if libgd is linked with libexif

[Tee0125]

orientation fix.

[cmb69]

Thanks! That would solve #341. Just a few quick remarks:

• if we apply auto-rotation/flipping, there should be a way to detect whether this happens; a constant may be sufficient
• there should be some tests
• the CMake build chain should also support this
• we already have gdImageFlipHorizontal|Vertical|Both, so no need to duplicate the functionality
• if we add functions combining rotation and flipping, these probably should be exposed
• the added rotation/flipping functions always create truecolor images, so copying the palette appears to be superflous

[Tee0125]

gdImageFlipHorizontal|Vertical|Both changes source image itself, but rotating 90/270 degree can not be implemented like that because image size need to be changed.

So for the consistency, I made a new functions for flipH/V which allocate a new image and copying pixels with horizontal/vertical flipping.

How about changing name of add functions to gdImageCloneRotate90/180/270/FlipH/FlipHRotate90/... , and move to gd.c? (Also applying palette copy, ... to renamed functions)

[vapier]

all of the rotate functions do the same thing except for the gdImageCreateTrueColor and gdImageSetPixel calls. imo we should create one internal static transformation function which all the others build off of with a callback to do the actual reindexing.

untested, but should show what i mean. hopefully the overhead of the callbacks isn't significant perf wise. it does make the code a lot easier to maintain imo.

typedef int (*rotateHelper)(gdImagePtr dst, int x, int y);

static gdImagePtr gdImageRotate(gdImagePtr src, int ignoretransparent, int newWidth, int newHeight, rotateHelper transX, rotateHelper transY)
{
...
    dst = gdImageCreateTrueColor(newWidth, newHeight);
...
        for (uY = 0; uY<src->sy; uY++) {
            int newY = transY(uY);
            for (uX = 0; uX<src->sx; uX++) {
                int newX = transX(uX);
...
                if (ignoretransparent && c == dst->transparent) {
                    gdImageSetPixel(dst, newX, newY, dst->transparent);
                } else {
                    gdImageSetPixel(dst, newX, newY, c);
                }
...
static int rot90x(gdImagePtr dst, int x, int y)
{
    return y;
}
static int rot90y(gdImagePtr dst, int x, int y)
{
    return dst->sy - x - 1;
}
gdImagePtr gdImageRotate90(gdImagePtr src, int ignoretransparent)
{
    return gdImageRotate(src, ignoretransparent, src->sy, src->sx, rot90x, rot90y);
}

[Tee0125]

@vapier : code is updated as you requested. please review again