s-trie classes refactored to generic trie with persistency

Squashed commit of the following:

commit e65dfc6dae119867bbf6be07f73ec912bc4da952
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Mon Oct 28 22:59:26 2013 -0400

    cleanup - old strie implementation removed

commit 32e168630ed77c930eb0375c68019d53f4357bbb
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Tue Oct 8 13:04:23 2013 -0400

    persistent trie - minor fixes

commit 67353374160afc7657f9e99c8a7a1610986752ef
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Sun Oct 6 23:54:48 2013 -0400

    generic trie with persistency - fixes; all relevant tests passed.

commit 6d66f76a77064193b88d4d2db5d9171c6b8e4962
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Sat Oct 5 00:04:21 2013 -0400

    generic trie with persistency - wip

commit edcef1a7abf7f046a1c8e4a4d6a9e8106cb13de5
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Mon Sep 30 21:37:24 2013 -0400

    actrie fixes; test cases for ac-trie completed

commit 56aa288ff67d08c5f8b63aa351cb4dfeabd68374
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Fri Sep 27 23:44:24 2013 -0400

    ac-trie: mostly done, test passed in s-trie compatibility mode

commit 126839479400e958f760dd5abfb731859d403037
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Sun Sep 22 23:56:49 2013 -0400

    ac-trie: work in progress

commit 426434a94ee8ca0bd2f5792ed4647aa759367391
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Thu Sep 19 22:05:42 2013 -0400

    minor fixes

commit 4dd94ca7ff5476d7bdbceca3b40c37e62e5f2b55
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Thu Sep 19 21:29:51 2013 -0400

    s-trie major refactoring