Revamp initial name collection functions to ensure proper argument ordering.

* src/names.c (NELT_NOOP): New constant
(name_elt) <next,prev>: New members.
(name_array,allocated_entries,entries,scanned): Remove.
(check_name_alloc): Remove function.
(name_elt_alloc): New static.
(name_list_adjust,name_list_advance): New functions.
(name_add_name,name_add_dir)
(name_add_file): Use new allocation functions.
(read_next_name): Advance list head pointer as necessary
before returning.
(name_next_elt): Read elements from list.
* tests/T-cd.at: New file.
* tests/T-mult.at: New file.
* tests/T-nest.at: New file.
* tests/Makefile.am: Add new testcases.
* tests/testsuite.at: Likewise.