Executable bits for install-tl

[jack]

My workflow whenever a new version of TL comes out is to use rsync to
clone the tlnet archive, and then run the `install-tl` script that's
contained in that clone to install TL from the local clone to a dir on my
machine.

I've noticed that when I do the initial rsyncing, `install-tl` isn't
executable.  This is despite the fact that I use the -E option with rsync.
 I think this means that the remote copy of `install-tl` isn't executable
(or else rsync would've made my local copy of it executable).

Can this be fixed?  Users should be able to just run ./install-tl after
rsyncing instead of having to mess with chmod.

Moreover, every time I use rsync to update my local clone of tlnet, the
executable bits for `install-tl` that I manually set will get removed. 
This is a pain, because then the user has to manually reset them if he
needs to re-install.

-jack