About the other skins, I can fix them once this patch gets merged.
The nice thing is that the old skins continue to work, however, no arrow buttons will be shown.
So yakuake will look like it used to, and scroll will only be working with the mouse wheel or shift+left/right.

OK, suggestions incorporated and hopefully I will not mess up again with arc.

Hopefully fixing the messed up previous commit.

• Improvements as suggested by alexeymin.

Done. Sorry again for the noise. Things should be working as expected now.

• Added tabbar scrolling support when the selected button cannot fit in the tabbar. Changed the way that the tabbar is getting drawn in order to support a scrollbar in the future. Now the buttons in the tabbar are all getting drawn in an off-screen private pixmap, called the buttonBar, and the buttonBar is getting scrolled as needed and painted to the widget at once.
• Added scroll buttons in the tabbar.
• Added support for the tabbar scroll buttons in the default (Breeze) theme.
• Selecting the correct tabs for double click actions

Grrrr! I messed up completely the patch with the arc tool.
Please don't test until I fix it. I will ping again. Sorry for the noise.

@alexeymin Thank you for helping me find the problem (with your arc patch tip).

• Updated corrupted png files.

@hein any possibility to get this merged? If not, any requested suggestions for improvements?

I can confirm that after this commit yakuake stays open when it is losing focus on X11.

@ngraham no worries about the authorship. You did at least as much for this patch, if not more when you include all the administrative work to get this patch landed :)

Another thing that I paid attention with this implementation is to not break existing skins. @alexeymin, as you might have noticed (hopefully if everything worked as intended) even if you couldn't see the arrow buttons with your selected skin, the skin looked as it used to. Moreover, the scrolling works in old skins, e.g. by using the mouse wheel button, even if there are no clickable arrow buttons.

This is how the updated default skin should look like:

Are you sure that the updated default skin is used?

@hein since this is a quite large commit that adds a new feature, I guess it is you who should decide if the implementation is acceptable or needs any modifications.

I don't have commit access so someone else should do it for me :)

@ngraham yes, vangelis@tasoulas.net is my primary e-mail, but my KDE identity still uses the cyberang3l@gmail.com e-mail (which is still valid).

@hein is this patch acceptable now to be committed?

Yes, this is a valid email address that you can use. Thank you :)

Is there any way to update the current diff?

How about the following?
Implements the zoom as Inkscape and Krita does: for more than 100% the zoom is increased by sqrt(2); for less than 100% the zoom is decreased by sqrt(0.5).

As long as the parameters of a function that is exposed via the QDBus interface are of a non-standard type such as int, QString etc, QDbus doesn't know how to handle them (kind of expected).
After some searching I believe that the correct way to handle such parameters is to register a new metatype for your special parameter and create marhalling/demarshalling functions as explained here: http://doc.qt.io/qt-5/qdbusargument.html#details
But this will need many more changes in the code.

Changed the commit to prevent breaking the existing DBus API based on the suggestions of @alexeymin.

@alexeymin yes, that's how it should be working.

This quite large commit is broken in three commits in the repository here: https://github.com/cyberang3l/yakuake/tree/scroll-tabs

Added scroll buttons in the tabbar as suggested by @alexeymin.
Added support for the tabbar scroll buttons in the default (Breeze) theme.

No, we don't have tabbar arrows at the moment.

Yes, lots of code already so let's see if this gets accepted first.
Before scrollbar comes in the UI, I see two more steps:

There was this conditional compilation with the following comment:

Here is a link with two JPG photographs: https://www.dropbox.com/s/ec7gmoerq4xf95a/test_gwenview_importer.tar?dl=0

I shoot with a Nikon D300 which clock is configured (usually) to UTC+1.

No commit access. Feel free to commit the changes.

Incorporated the changes suggested by Christoph Feck.

In the first patch I had just changed the accepted parameter of the "Exiv2ImageLoader::load()" function from QByteArray& to QString.
But code that expects this function to accept a QByteArray exists in different parts of the software. In this updated patch I just added a second instance of the function "Exiv2ImageLoader::load()" without removing the original one.