Updating basictex did not trigger format rebuild

[Karl Berry]

    ran "sudo tlmgr paper a4". 

Not that I know anything anymore :), but I think it's actually desirable
that tlmgr paper always rebuilds formats, irrespectively of
create_formats. Because in that case the user is explicitly asking to do
something (change paper size) which definitely requires remaking the
formats.

Whereas downloading packages only implicitly requires new formats, so it
sort of makes sense for that be controlled by the option.  Although, as
we've seen, disabling remaking formats on package updates is not likely
to do anything but cause confusion in the few cases where it actually
makes a noticeable difference.

I think we originally had that option only for installation time,
because it is plausible, if unusual, to not create all formats
automatically at the end of installation, e.g., to allow for intervening
local tweaking of packages or setup. I sometimes disable create_formats
for myself, and let the formats be created on the fly (with mktexfmt),
just to make sure that that feature still works, and also so only the
formats I actually use get created.

So, Norbert, maybe it would be better for package updates to also ignore
create_formats, and for it only to apply at installation? Wdyt? --thanks, k.