Closes: #1566

Short names were used in win32 implementation to allow launching
on installations where full path to libgio-2.0-0.dll contain spaces.
However, short names are optional on windows: so if they were disabled
that method fails - see issue linked above.

Since rundll32 doesn't support neither spaces, nor quotes in cmdline
this patch changes rundll32 argument to just .\gio-dll-name.dll
and uses the entire path directory containing gio dll as rundll32
current directory.

Added comments informing about potential subtleties discovered during
writing test for gdbusaddress on win32.
There are not known to have real-world user-visible effect,
so by now I'm only adding comments without creating issues.