Fork before performing tcpwrappers check.

Don't rely on nonstandard bsd_signal() function, instead
 require that the platform has sigaction().  This is 2001,
 after all.  This may resolve some potential portability
 problems.

Log a message if memory allocation fails, instead of dying silently.

Clean up the main dispatch loop.

Use <sysexits.h> for exit codes, if it exists.

Reformat tftpd.c to match the other files.

tftp/tftpsubs.h

@@ -42,6 +42,9 @@
  * Prototypes for read-ahead/write-behind subroutines for tftp user and
  * server.
  */
+#ifndef TFTPSUBS_H
+#define TFTPSUBS_H
+
 #include <stdlib.h>
 
 struct tftphdr *r_init(void);
@@ -62,3 +65,5 @@ extern int segsize;
  */
 extern void *xmalloc(size_t);
 extern char *xstrdup(const char *);
+
+#endif