[RFC] separate .git from working directory

Hi, I was thinking about this while reading subproject thread. In a simple case, I have a repo A located at ~/project-a and another repo B located at ~/project-a/some/dir/project-b. With this setup, command "find" and other directory-recursive commands will run horribly from ~/project-a when they go inside project-b/.git (no I don't want to repack -d everytime I want to find something). I propose to move project-b/.git outside and place a file, say .gitdir, in project-b directory. git-sh-setup and setup_git_directory are taught to recognize .gitdir, read it to find the actual GIT_DIR recorded inside .gitdir. This way git commands inside project-b should work fine while I can "find ~/project-a -name blah" or "grep -R blah" quickly. .gitdir format could be a simple shell-like format with environment variable assignments. BTW, talking about subproject support, how about git be taught to ignore directories which contain .gitdir so that git commands will not waste time checking project-b directory?