refs #5103. Force Uninstall added to NSIS script.

Code/Mantid/Build/CMake/NSIS.template.in

@@ -36,6 +36,8 @@
 
   ;Set compression
   SetCompressor @CPACK_NSIS_COMPRESSOR@
+  
+  SetOverwrite @CPACK_NSIS_FORCE_OVERWRITE@
 
 @CPACK_NSIS_DEFINES@   
 

Code/Mantid/Build/CMake/WindowsNSIS.cmake

@@ -14,8 +14,10 @@
 	set( CPACK_INSTALL_PREFIX "/")
 	set( CPACK_NSIS_DISPLAY_NAME "Mantid${CPACK_PACKAGE_SUFFIX}")
 	set( CPACK_PACKAGE_NAME "Mantid${CPACK_PACKAGE_SUFFIX}" )
-	set( CPACK_PACKAGE_INSTALL_DIRECTORY "MantidInstall${CPACK_PACKAGE_SUFFIX}")
+	set( CPACK_PACKAGE_INSTALL_DIRECTORY "MantidInstall${CPACK_PACKAGE_SUFFIX}") 
 	set( CPACK_NSIS_INSTALL_ROOT "C:")
+	set( CPACK_NSIS_FORCE_OVERWRITE on CACHE STRING "Force installer to overwrite any existing install")
+	set_property(CACHE CPACK_NSIS_FORCE_OVERWRITE PROPERTY STRINGS on off)
 
 	#set( CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL "ON")
 	set( CPACK_PACKAGE_ICON "${CMAKE_CURRENT_SOURCE_DIR}/Images\\\\MantidPlot_Icon_32offset.png" )