<top level>: Update Copyright years. Add prototype for xmalloc.

<top level>: Update Copyright years.  Add prototype for xmalloc.
(find_file): Accept 3 arguments PATH_VAR, FULL_FNAME, and FULL_LEN
instead of an LPOFSTRUCT pointer.  Use xmalloc instead of malloc.
Loop over an array of extensions, instead of duplicating the same
code inline.  Use SearchPath followed by CreateFile, instead of
the obsolete OpenFile.  Fixes Savannah bug #17277.
(process_begin): Find $(PATH) in `envp', and pass a pointer to it
to `find_file'.  Fixes Savannah bug #25662.