updated Norwegian translation

For an unknown reason the Norwegian.nsh and the NorwegianNynorsk.nsh files of NSIS 3 misses the entries

!ifdef MULTIUSER_INSTALLMODEPAGE
${LangFileString} MULTIUSER_TEXT_INSTALLMODE_TITLE
${LangFileString} MULTIUSER_TEXT_INSTALLMODE_SUBTITLE
${LangFileString} MULTIUSER_INNERTEXT_INSTALLMODE_TOP
${LangFileString} MULTIUSER_INNERTEXT_INSTALLMODE_ALLUSERS
${LangFileString} MULTIUSER_INNERTEXT_INSTALLMODE_CURRENTUSER
!endif

I added them in the attached patch and the Norwegian translator of the GPLed program "LyX" translated the messages. He agreed to send you this patch.