replace blist_fill with list_alloc_all

[dougm]

Summary

The only use of blist_fill is one that uses it to allocate all the free blocks at once. This can be implemented trivially, and quickly, by accessing only the root node. Define blist_alloc_all to do that, and discard blist_fill. Use blist_alloc_all in place of blist_fill.

[dougm]

Add an alloc-all option to the test program.

[dougm]

Correct update of swap_pager_avail.