[Qt-creator] Custom plugin search path?

[Guido Seifert]

> PluginManager::setPluginPaths already searches the directories for plugins, so it would be preferable to only call that once with all plugin paths.
> Otherwise fine.

Ahhh, cowardly me. I just tried to change as little as possible. Adding stuff without
changing existing code. :-)

Do you like this one better: 
http://pastebin.com/i8RkVTYf

Had to move the path evaluation code below the commandline evaluation code. And
QStringList pluginPaths isn't const anymore. But setPluginPaths is called only once.

Guido