[Neil Jerram] "avoid running GC when SCM_I_CURRENT_THREAD is unset"

[Neil Jerram]

[sorry, this should of course have been CC'd to the list too...]

Hi Andy,

I saw this change and couldn't fully understand it.  Given that you
ended up adding GC_disable() and GC_enable() around the GC_malloc()
call, couldn't you just have done that without all the other changes
from "t->" to "t." ?

I'm probably missing something, but could you point it out?

Thanks,
        Neil