talloc: Tune talloc_vasprintf

vsnprintf is significantly more expensive than memcpy. For the
common case where the string we print is less than a kilobyte, avoid
the second vsnprintf.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu May 15 12:49:14 CEST 2014 on sn-devel-104
add FSCTL_SET_ZERO_DATA fsctl define

fallocalte with the FALLOC_FL_ZERO_RANGE flag introduced
with Linux 3.15 should be able to do this soon

Signed-off-by: Bjoern Jacke <bj@sernet.de>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
add FSCTL_SET_ZERO_ON_DEALLOCATION define

Signed-off-by: Bjoern Jacke <bj@sernet.de>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

Autobuild-User(master): Björn Jacke <bj@sernet.de>
Autobuild-Date(master): Thu May 15 15:16:34 CEST 2014 on sn-devel-104