[MERGE][#230567] Faster (local) branch

[Andrew Bennetts]

Robert Collins wrote:
[...]
> 
> It was an experimental branch Aaron and I created in London a couple of
> years back; at that time we didn't see a performance gain - but a
> smaller delta now will show up more - we have moved the goalposts a long
> way.
> 
> however - os.open() still honours umask, which as I recall is why we
> discarded the branch.

umasks don't cause the execute bit to be set by default, though:

$ umask 0000
$ touch 0000
$ umask 0777
$ touch 0777
$ ls -l
total 0
-rw-rw-rw- 1 andrew andrew 0 2008-05-29 11:36 0000
---------- 1 andrew andrew 0 2008-05-29 11:36 0777

-Andrew.