[krbdev.mit.edu #6200] Eliminate use of "unsafe" functions

[Greg Hudson via RT]

Audit tools such as lint and Coverity's SECURE_CODING checker flag all
uses of functions which are often used unsafely.  For Coverity, these
include strcpy, strcat, sprintf, all *scanf variants, random, lrand48,
and rand.

Although these functions are used safely within the krb5 code base to
the best of our knowledge, their use is undesirable because ensuring
their safety requires manual investigation each time the code base is
audited (by us or by others).  This ticket will track the process of
eliminating these uses.