Get test coverage to 100%

[slott56]

Current state (approximately)

Name                       Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------------------
py_rete/alpha.py              12      0      2      0   100%
py_rete/beta.py               23      0      2      0   100%
py_rete/bind_node.py          24      0      8      0   100%
py_rete/common.py            135     27     68      7    77%   63, 83, 132, 138-162, 216->215, 221->223, 224, 228-231, 235->exit
py_rete/conditions.py         97     14     46      5    80%   36, 46, 50, 56, 58, 60, 129, 137, 140, 148, 155, 170, 173, 190
py_rete/fact.py               68     20     36      6    65%   29, 34, 54, 67, 71, 85, 91, 94-109
py_rete/filter_node.py        19      0      6      0   100%
py_rete/join_node.py          78      3     44      1    97%   89, 93-94
py_rete/ncc_node.py           41      5     12      3    85%   34, 40-42, 43->exit, 79
py_rete/negative_node.py      38      2     20      1    95%   30, 35
py_rete/network.py           370     69    222     26    78%   63, 77, 85-95, 98-148, 155, 160-162, 178, 180->184, 187, 202->201, 205, 228, 249, 268, 301->298, 319, 325->327, 369-371, 387->385, 396-397, 411, 427, 436, 464->467, 477-478, 488->487, 492->491, 494->exit, 513
py_rete/pnode.py              25      3      8      1    82%   32->exit, 36-38
py_rete/production.py        106     14     71     10    81%   31, 42, 50, 64, 76-82, 88-89, 134, 139->142, 145->148, 152, 160
----------------------------------------------------------------------
TOTAL                       1036    157    545     60    81%

Two lines in bind_node.py have been tested.

The line numbers reflect adding some module docstrings and modifying class docstrings, so they may not match the current source files as of this issue's creation time.