Change uses of scm_is_simple_vector to scm_is_vector

Change uses of scm_is_simple_vector to scm_is_vector

* libguile/filesys.c, libguile/random.c, libguile/stime.c, libguile/trees.c,
  libguile/validate.h: use scm_is_vector instead of scm_is_simple_vector.
* libguile/sort.c (scm_sort_x, scm_sort, scm_stable_sort_x)
  (scm_stable_sort): Remove scm_is_vector check; scm_is_array is
  sufficient.
* test-suite/tests/arrays.test: Fix header.
* test-suite/tests/random.test: New coverage test covering
  random:normal-vector!.
* test-suite/Makefile.am: Include random.test in make check.