[PATCH 0 of 4 STABLE] isolation between each local repositories handled in a same process at a time

[FUJIWARA Katsunori]

This patch series fixes some problem about isolation between each
local repositories handled in a same process at a time.

I posted this series as STABLE, because this is a kind of bug fix.

But this may be suitable for DEFAULT, because this is a little tricky,
especially #3 and #4.

If this series is applied on DEFAULT, patch #3 will cause conflict,
and #4 will cause putting tests into unexpected location in
"tests/test-largefiles.t".

So, I'll repost one for DEFAULT, if this should be queued to DEFAULT.