* On Cygwin, similar to Windows, "git push //server/share/repository"

ought to mean a repository on a network share that can be accessed

locally, but this did not work correctly due to stripping the double

slashes at the beginning.

* The progress meter did not give a useful output when we haven't had

0.5 seconds to measure the throughput during the interval. Instead

show the overall throughput rate at the end, which is a much more

useful number.

* We run an early part of "git gc" that deals with refs before

daemonising (and not under lock) even when running a background

auto-gc, which caused multiple gc processes attempting to run the

early part at the same time. This is now prevented by running the

early part also under the GC lock.

Also contains a handful of small code and documentation clean-ups.