[PATCH] git-mv is not able to handle big directories

When moving directory with large number of files git-mv says:

git-mv jsp* .

Can't exec "git-update-index": Argument list too long at /usr/local/bin/git-mv 
line 193.
git-update-index failed to add new names with code -1

This patch fixes this by building list of files with limited len (currently 
5000) and executing git-update-index few times until all files will be 
processed. I don't know how to determinate limit of command line but 5000 
seems safe enougth to me.