When `git clone` is asked to dissociate the repository from the
reference repository whose objects were used, it is quite possible that
the pack files need to be repacked. In that case, the pack files need to
be deleted that were originally hard-links to the reference repository's
pack files.

On platforms where a file cannot be deleted if another process still
holds a handle on it, we therefore need to take pains to release all
pack files and indexes before dissociating.

This fixes https://github.com/git-for-windows/git/issues/446

The test case to demonstrate the breakage technically does not need to
be run on Linux or MacOSX. It won't hurt, either, though.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

On Windows, files that are in use cannot be removed or renamed. That
means that we have to release pack files when we are about to, say,
repack them. Let's introduce a convenient function to close all the
pack files and their idx files.

While at it, we consolidate the close windows/close fd/close index
stanza in `free_pack_by_name()` into the `close_pack()` function that
is used by the new `close_all_packs()` function to avoid repeated code.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

There was a lot of repeated code to close the file descriptor of
a given pack. Let's just refactor this code into a single function.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

On Windows, dissociating from a reference can fail very easily due to
pack files that are still in use when they want to be removed.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Signed-off-by: Junio C Hamano <gitster@pobox.com>