ADWIN: tests for BucketRow and BucketRowList methods

[macandleighs]

Write tests for the other BucketRow and BucketRowList methods, separate from the full ADWIN tests. Currently, the relevant test functions that exist are: test_bucket_row_init, test_bucket_row_list_empty, and test_bucket_row_list_append_head.

Methods in BucketRow still to write tests for

add_bucket remove_buckets shift

Methods in BucketRowList still to write tests for

init append_tail remove_tail

[tms-bananaquit]

An alternative would be to switch to a native Python data structure that can implement a linkedlist, instead of the current "by-hand" implementation, which would avoid the unit tests altogether. It'd likely be more efficient, too.