Much better solution to avoid the gtk+ style on Linux

Thiago showed me how to find out which style is in use and if we see a
user is running gtk+ we simply switch Subsurface to Oxygen (using the
old plastique in the previous patch was a result of reading an old Qt
book, I guess).

Solved-by: Thiago Macieira <thiago@macieira.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

qt-gui.cpp

@@ -30,6 +30,8 @@
 #include <QTranslator>
 #include <QSettings>
 #include <QDesktopWidget>
+#include <QStyle>
+#include <QDebug>
 
 const char *default_dive_computer_vendor;
 const char *default_dive_computer_product;
@@ -84,17 +86,14 @@ const char *getSetting(QSettings &s, QString name)
 void init_ui(int *argcp, char ***argvp)
 {
 	QVariant v;
-#ifdef __linux__
-	// for people running under Gnome the default style is
-	// really ugly; this seems like a bad hack, but it makes
-	// things look somewhat better
-	// I'd much rather be able to check if it is using the Gnome
-	// style and only then force plastique but I haven't been
-	// able to figure out how to do that
-	QApplication::setStyle("plastique");
-#endif
+
 	application = new QApplication(*argcp, *argvp);
 
+	// the Gtk theme makes things unbearably ugly
+	// so switch to Oxygen in this case
+	if (application->style()->objectName() == "gtk+")
+		application->setStyle("Oxygen");
+
 #if QT_VERSION < 0x050000
 	// ask QString in Qt 4 to interpret all char* as UTF-8,
 	// like Qt 5 does.