Add MumbleApplication::applicationVersionRootPath().

Also add MumbleApplication::instance() for easily getting
the MumbleApplication singleton.

src/mumble/MumbleApplication.cpp

@@ -36,6 +36,10 @@
 #include "GlobalShortcut.h"
 #include "Global.h"
 
+MumbleApplication *MumbleApplication::instance() {
+	return static_cast<MumbleApplication *>(QCoreApplication::instance());
+}
+
 MumbleApplication::MumbleApplication(int &pargc, char **pargv)
     : QApplication(pargc, pargv) {
 	
@@ -45,6 +49,14 @@ MumbleApplication::MumbleApplication(int &pargc, char **pargv)
 	        Qt::DirectConnection);
 }
 
+QString MumbleApplication::applicationVersionRootPath() {
+	QByteArray versionRoot = qgetenv("MUMBLE_VERSION_ROOT");
+	if (versionRoot.count() > 0) {
+		return QString::fromUtf8(versionRoot.constData());
+	}
+	return this->applicationDirPath();
+}
+
 void MumbleApplication::onCommitDataRequest(QSessionManager &) {
 	// Make sure the config is saved and supress the ask on quit message
 	if (g.mw) {

src/mumble/MumbleApplication.h

@@ -44,8 +44,31 @@ class MumbleApplication : public QApplication {
 #endif
 		Q_OBJECT
 	public:
+
+		/// The instance function returns an instance
+		/// of the MumbleApplication singleton.
+		static MumbleApplication *instance();
+
 		MumbleApplication(int &pargc, char **pargv);
-		
+
+		/// applicationVersionRootPath returns
+		/// Mumble's "versioned root"-path.
+		///
+		/// This is a version-specific path that contains
+		/// supplementary binaries and other products
+		/// that Mumble needs to function.
+		///
+		/// In the current implementation, the versioned
+		/// root path is set by the MUMBLE_VERSION_ROOT
+		/// environment variable. This environment variable
+		/// is set in the mumble.exe launcher.
+		///
+		/// If a versioned root path has not been
+		/// configured in the environment, the function
+		/// returns the same path as Qt's own
+		/// QApplication::applicationDirPath().
+		QString applicationVersionRootPath();
+
 		bool event(QEvent *e) Q_DECL_OVERRIDE;
 #ifdef Q_OS_WIN
 # if QT_VERSION >= 0x050000