Fix compiler invocation, CXXFLAGS, and installation procedure.

Index: Makefile
--- Makefile.orig
+++ Makefile
@@ -1,5 +1,3 @@
-CC=g++
-CCFLAGS=-O2 -Wall
 CFILES=game.cpp gamestate.cpp gui.cpp image.cpp main.cpp panel.cpp player.cpp resources.cpp screen.cpp sector.cpp sound.cpp tutorial.cpp utils.cpp TinyXML/tinyxml.cpp TinyXML/tinyxmlerror.cpp TinyXML/tinyxmlparser.cpp
 HFILES=game.h gamestate.h gui.h image.h panel.h player.h resources.h screen.h sector.h sound.h tutorial.h utils.h common.h stdafx.h TinyXML/tinyxml.h
 OFILES=game.o gamestate.o gui.o image.o panel.o player.o resources.o screen.o sector.o sound.o tutorial.o utils.o main.o TinyXML/tinyxml.o TinyXML/tinyxmlerror.o TinyXML/tinyxmlparser.o
@@ -12,27 +10,27 @@ LIBS=-lSDL2_image -lSDL2_mixer
 all: $(APP)
 
 $(APP): $(OFILES) $(HFILES) $(CFILES)
-	$(CC) $(OFILES) $(CCFLAGS) $(LINKPATH) $(LIBS) -o $(APP)
+	$(CXX) $(OFILES) $(CCFLAGS) $(LINKPATH) $(LIBS) -o $(APP)
 
 .cpp.o:
-	$(CC) $(CCFLAGS) -O2 $(INC) -c $< -o $@
+	$(CXX) $(CXXFLAGS) $(INC) -c $< -o $@
 
 # REMEMBER to update debian/dirs if the system directories that we use are changed!!!
 install: $(APP)
-	mkdir -p $(DESTDIR)/opt/gigalomania # -p so we don't fail if folder already exists
-	cp $(APP) $(DESTDIR)/opt/gigalomania
-	cp readme.html $(DESTDIR)/opt/gigalomania
-	cp -a gfx/ $(DESTDIR)/opt/gigalomania # -a need to copy permissions etc
-	cp -a islands/ $(DESTDIR)/opt/gigalomania
-	cp -a music/ $(DESTDIR)/opt/gigalomania
-	cp -a sound/ $(DESTDIR)/opt/gigalomania
+	mkdir -p $(PREFIX)/share/gigalomania # -p so we don't fail if folder already exists
+	cp $(APP) $(PREFIX)/bin/gigalomania
+	cp readme.html $(PREFIX)/share/gigalomania
+	cp -a gfx/ $(PREFIX)/share/gigalomania # -a need to copy permissions etc
+	cp -a islands/ $(PREFIX)/share/gigalomania
+	cp -a music/ $(PREFIX)/share/gigalomania
+	cp -a sound/ $(PREFIX)/share/gigalomania
 	# needed for DESTDIR option:
-	mkdir -p $(DESTDIR)/usr/share/applications
-	cp gigalomania.desktop $(DESTDIR)/usr/share/applications/
+	mkdir -p $(PREFIX)/share/applications
+	cp gigalomania.desktop $(PREFIX)/share/applications/
 	#cp gigalomania_fullscreen.desktop $(DESTDIR)/usr/share/applications/
 	# needed for DESTDIR option:
-	mkdir -p $(DESTDIR)/usr/share/pixmaps
-	cp gigalomania64.png $(DESTDIR)/usr/share/pixmaps/
+	mkdir -p $(PREFIX)/share/pixmaps
+	cp gigalomania64.png $(PREFIX)/share/pixmaps/
 # REMEMBER to update debian/dirs if the system directories that we use are changed!!!
 
 uninstall:
