Add on-launch code to set Document Icon in windows registry

Since OpenSCAD doesn't distribute with additional image files, this means a new icon needs to be built into the .exe. This is accomplished by adding a line to the end of openscad_win32.rc file consisting of something like the following:
IDI_ICON2 ICON DISCARDABLE "icons/openscad_doc.ico"
which will get built into the exe as icon index 1 (icon index 0 is the current app icon.)

In the cmdline and gui functions in openscad.cc I added code to set the HKEY_CURRENT_USER/Software/Classes/OpenSCAD_File/DefaultIcon/Default value to the icon index 1 of openscad.exe

	modified:   openscad_win32.rc
	modified:   src/openscad.cc

openscad_win32.rc

@@ -33,5 +33,6 @@ VS_VERSION_INFO VERSIONINFO
 /* End of Version info */
 
 IDI_ICON1   ICON    DISCARDABLE "icons/openscad.ico"
+IDI_ICON2   ICON    DISCARDABLE "icons/openscad_doc.ico"
 
 

src/openscad.cc

@@ -43,6 +43,8 @@
 #include "CocoaUtils.h"
 #include "FontCache.h"
 
+#include <QDir>
+
 #include <string>
 #include <vector>
 #include <fstream>
@@ -318,6 +320,12 @@ int cmdline(const char *deps_output_file, const std::string &filename, Camera &c
 	parser_init();
 	localization_init();
 
+#ifdef Q_OS_WIN
+    QSettings reg_setting(QLatin1String("HKEY_CURRENT_USER"), QSettings::NativeFormat);
+    QString appPath = QDir::toNativeSeparators(app.applicationFilePath() + QLatin1String(",1"));
+    reg_setting.setValue(QLatin1String("Software/Classes/OpenSCAD_File/DefaultIcon/Default"),QVariant(appPath));
+#endif
+
 	Tree tree;
 #ifdef ENABLE_CGAL
 	GeometryEvaluator geomevaluator(tree);
@@ -664,6 +672,12 @@ int gui(vector<string> &inputFiles, const fs::path &original_path, int argc, cha
 	installAppleEventHandlers();
 #endif
 
+#ifdef Q_OS_WIN
+    QSettings reg_setting(QLatin1String("HKEY_CURRENT_USER"), QSettings::NativeFormat);
+    QString appPath = QDir::toNativeSeparators(app.applicationFilePath() + QLatin1String(",1"));
+    reg_setting.setValue(QLatin1String("Software/Classes/OpenSCAD_File/DefaultIcon/Default"),QVariant(appPath));
+#endif
+
 #ifdef OPENSCAD_UPDATER
 	AutoUpdater *updater = new SparkleAutoUpdater;
 	AutoUpdater::setUpdater(updater);
@@ -901,4 +915,3 @@ int main(int argc, char **argv)
 
 	return rc;
 }
-