Merge branch 'ad/cygwin-wants-rename' into maint

Merge branch 'ad/cygwin-wants-rename' into maint

On Cygwin, object creation uses the "create a temporary and then
rename it to the final name" pattern, not "create a temporary,
hardlink it to the final name and then unlink the temporary"
pattern.

This is necessary to use Git on Windows shared directories, and is
already enabled for the MinGW and plain Windows builds.  It also
has been used in Cygwin packaged versions of Git for quite a while.
See http://thread.gmane.org/gmane.comp.version-control.git/291853
($gmane/275680, $gmane/291853).

* ad/cygwin-wants-rename:
  config.mak.uname: Cygwin needs OBJECT_CREATION_USES_RENAMES