in d444fd2 I forgot to rename HAVE_ERR to HAVE_ERRC too.

while here also fix the prototypes for warn and warnx

while here also rearrange a bit the compl_state_reset/compl_add_entry dance and do the allocations only in the latter.

Since d3e1ab0 kamiftp started to issue Twalks over ".". walk(9p) (from plan9ports) says that The name ``.'' (dot), meaning the current directory, is not used in the protocol. hinting that it shouldn't be used, and thus kamid rejects it. It's also redundant since it's always possible to do a walk to duplicate the directory fid instead of walkig "." which is what kamiftp now does.

don't use funopen(3) as it's not portable, found the hard way by cage. libbsd provides a funopen(3) on top of GNU libc' fopencookie, but I'd like to avoid dependencies on functions that are hard to port to other platforms.