POL_Install_dotnet45

Issues for this script have been reported within the ticket #5572.

The originial ticket is about a download issue (workaround exists). The script does not install, however on 3.5 part due to a registry issue causing some kind of loop...

Workaround:

1) Make sure you are running on Windows-7 (unfortunately the default is still Windows XP) using winecfg

2) Make sure you have dotnet40 script succesfully run (you need to workaround the download problem, copy dotnet30 manually into your playonlinux ressources folder)

3) Download 4.5.1 (not the one from this script) installer. Offline Installer URL can be found on wine page:

https://appdb.winehq.org/objectManager.php?sClass=version&iId=25478

4) Install manually running a .exe for your wanted virtual drive (PlayOnLinux configuration tab misc).

explicitly test for 64bit (redundant as called scripts also test, but sort of documenting the incompatibility - and better crash early)
set variables as local to avoid collisions with calling script

do not set $TITLE (does not make sense in a "function" script)
download installer as resource so it's cached (and also avoid collisions with calling script's $POL_System_TmpDir)

Switched to newer shell declaration

Wow. I am dumb. I forgot the shell declaration at the top. :\

Quick question; should even the functions have the 

declaration instead? 

Initial commit.