[krbdev.mit.edu #2961] missing dependencies in util/ss

[Ken Raeburn via RT]

Some dependencies are missing from the Makefile.in in util/ss, which
can cause occasional build failures depending on the order in which
make chooses to build things.  In particular, std_rqs.c (a generated
file) needs ss_err.h (another generated file) in order to build.

Fixed on trunk in:
  util/ss/ChangeLog    1.73
  util/ss/Makefile.in  1.53