Add hook to end of `custom-create-buffer-internal'

[Drew Adams]

Not a bug, but an enhancement request. 

Please a new hook, say, `custom-buffer-create-hook', and run it at the
end of `custom-create-buffer-internal'. This is for things to be done
_after_ the buffer has been filled with its text. An example: a
function to fit a one-window frame to the buffer contents.