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

[Andrew Bennetts]

Andrew Bennetts wrote:
> Robert Collins wrote:
[...]
> > 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:
[...]

I should have added that the umask does control the 'x' bit when making
directories, but I presume we don't care about that.

-Andrew.