tests/test-config-case.t

largefiles: respect store.createmode and avoid extra file copy

Before, a tempfile was used to create a temp file was created with 600
permissions and the uploaded data was written into it. This file was
then *copied* to .hg/largefiles/<hash>.

We now simply use atomictempfile to write the data to a temp file with
the right permissions and then rename that into place.

  $ echo '[Section]' >> $HGRCPATH
  $ echo 'KeY = Case Sensitive' >> $HGRCPATH
  $ echo 'key = lower case' >> $HGRCPATH

  $ hg showconfig Section
  Section.KeY=Case Sensitive
  Section.key=lower case