Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

elsewhere as well.

Also trim another eight bytes from vsprintf.o.  :)

Shaved around 100 bytes off vsprintf.o.  It's now 50 bytes smaller than
the old implementation and provides much more conformant semantics,
including the ability to return the number of characters that would have
been printed to the string had the buffer been big enough.  (iSCSI needs
this functionality).

compile, even if it won't yet be safe.