* etags.c (xmalloc, xrealloc): Accept size_t, not unsigned int,

* etags.c (xmalloc, xrealloc): Accept size_t, not unsigned int,

to avoid potential buffer overflow issues on typical 64-bit hosts.
(whatlen_max): New static var.
(main): Avoid buffer overflow if subsidiary command length is
greater than BUFSIZ or 2*BUFSIZ + 20. Do not use sprintf when its
result might not fit in 'int'.