wc: read and process --files0-from= input a name at a time,

wc: read and process --files0-from= input a name at a time,

when the file name list is not too large.  Before, wc would always read
the entire file name list into memory and *then* process each file name.
wc does read the list into memory when the list is known not to be too
large; this is done in order to be able to align the output numbers,
as it does with arguments specified on the command-line
* src/wc.c: Include "argv-iter.h".
(main): Rewrite to use argv-iter when the input file name list
is known to be too large.
* NEWS (Bug fixes): Mention it.