preliminary patch for better POSIX installs

[pabs]

Hi all,

nsis doesn't currently install like a normal Unix program - instead it dumps all its stuff in one directory with a few subdirectories. At the moment for the debian package I hack around this by moving files around after the install.

The attached patch against CVS gets about 50% of the way to a better install structure. One problem is that only the subs and makensis get installed when I do scons install. It contains proper DESTDIR (useful for packages), PREFIX and so on semantics, and a portability switch for Windows, where the plugins/etc are stored relative to the exe.

So, I would like to know if this is the kind of thing that should be in the official nsis package. Also, could people review the patch to make sure I'm using scons right, and that I have not done anything stupid.