move the first d() initialiser back into hook_drush_init() and

document

this really doesn't belong to _provision_drush_check_load() at all,
which looks at sys_getloadavg()...

i am not sure the comment is accurate, but it's based on commit
archeology dating back from 2010, see commits:

0c4d648d
f7b8dabe

this was done trying to track down #2281983