Fix our Scintilla patch

It got broken by df589a9d52086b22fe1dc7591482f5aa8f9bbc0e -- you have
to fix the line change count in the block header too.
Use GLib's portable version gethostname(): g_get_host_name()

Drop our own portability layer and use GLib's one instead (which
actually does exactly the same as our own).

Thanks to Matthew for spotting this.
Use empty string on win32 when no print command

In the preferences dialog it would show a single
quote because the print command couldn't be found
and the NULL prematurely terminated the g_strconcat()
call, leaving a single quote in the print command
entry.

Thanks to Lex for finding where the problem was.