v0.9.3
Add per-file error identifiers
Add PXE FILE API.
!PXE and PXENV+ structures are in code segment, not data segment.
Add pxe_set_cached_filename() so that pxe_tftp.c can also update the stored DHCP packets.
Start restructuring pxe_tftp.c to cope with multicast (MTFTP) receives.
Use XFER_INIT() macro.
Fix compiler warnings that appear only on OpenBSD.