Separately track the number of items in alloc_table in a variable. With

Separately track the number of items in alloc_table in a variable. With
the changes for handling template files in r1.293, alloc_table became
a pointer to an array of structs (rather than the array itself), so
nitems(alloc_table) no longer returns the number of elements. As found
by sebastia@, autosize would only try the first allocation scheme,
so installation would fail on small disks.  ok henning@