parts of unif.[ch] to array-handle.[ch]

parts of unif.[ch] to array-handle.[ch]

* libguile/array-handle.c:
* libguile/array-handle.h: Move some parts of unif.c and unif.h to these
  new files.

* libguile/unif.c:
* libguile/unif.h: Update includers. Since unif.h depends on the array
  handle type, we include array-handle.h, which also means that there
  will be no difference for our callers.

* libguile/init.c: Call scm_init_array_handle, though it does nothing as
  of yet.

* libguile/Makefile.am: Adapt for new files.