Trouble with building showtime.

Hello all.

I recently installed psl1ght by following this:

http://psl1ght.net/wiki/TutorialInstall:CygWin

I then installed:

https://github.com/andoma/PSL1GHT

Now I am trying to build showtime and I get this error:

POD@POD /home/pod/showtime-master
$ ./configure.ps3
fatal: /usr/lib/git-core/git-submodule cannot be used without a working tree.
Updating libav, submodule status =
fatal: /usr/lib/git-core/git-submodule cannot be used without a working tree.
Configuring libav...
support/configure.inc: line 328: /home/pod/showtime-master/ext/libav/configure: No such file or directory
Configure failed

I guess I need a working tree but I don't know what that is.

Will someone please explain this to me?