This is aimed at allowing a stride to optionally be
given for the parameter name array... this will allow
use of lws_struct metadata as the parameter name
array.
Also introduce the option to put all allocations in
an lwsac instead of via lws_mallocs.
If you just want a "file" in multipart, don't care about the length or
anything else, then you don't need any params tables and associated
allocations.
Audit all lws_hdr_copy() usages inside lws and make sure we
take care about it failing.
Also since the patch around aggregation of headers by ',',
lws_hdr_copy() needs a little more space in the output buffer,
adjust one place where that caused it to start failing in an
exact-sized buffer.
