Fixes #1546

struct worker for "usual stuff" like vsl, stats etc.

function arguments.

single time, and it is inconsistent with how we do it elsewhere.

begining with the ObjIter set.  Have them consistently take objcore
as first argument and replace "struct objiter*" into a void* cookie
of the stevedores choice.

interface to stevedores.

Fixes: #1591

Fixes: #1592

Require that buffer arguments have greater than zero length to allow
for zero termination.

Make sure that NULL buffers are not touched.

what we really want with them.

Now I just need to figure out where to stuff them.

dependent (is there a C-L header ?), and semantic (ie:  HEAD request
doesn't have body, even if the response has C-L etc.)

Spotted by:	Dridi Boukelmoune