[PATCH 0 of 2 V2] localrepo: eliminate os.unlink call in wwrite

[Adrian Buehlmann]

Previous version of this series:

  http://markmail.org/thread/f4x6mfynclck7yas

Changes to previous version:

I've picked up Matt's proposal to always reset the flags
on 'w'rite in the opener, as he wrote in message

  http://markmail.org/message/hs53z7lqplqwbjaq

I think that proposal makes sense.

With the refactoring 6ff784de7c3a, the opener already stopped
preserving symlinks on 'w'rite. Now, we also stop preserving flags
on normal files on 'w'rite.

This keeps the opener minimal and fast.

The first patch renders the os.unlink call in wwrite redundant and the
second patch removes it.

Testsuite passed on Ubuntu Linux (patches applied to 5dac0d04b838).