gsim/base:

Minor corrections to `disaggregate_poe` in GSIM base class. If an index
referenced the last epsilon bin, a zero value was returned. Now, the correct
non-zero PoE value is computed.
gsim/base_test:

Corrected expected value for PoE corresponding to an IML in the last bin.
acceptance/disagg_test:

Correct expected matrix value for acceptance test.
calc/disagg:

Removed `joint_probs` from `_collect_bins_data`. This is not used with the new
corrected equation.
calc/disagg:

Corrected disaggregation implementation, based on the new equation.
tests/calc/disagg_test:

Fixed broken tests and updated expected results where necessary.
calc/disagg:

Corrected implementation of PMF extractors, per the new equation. Tests are
broken, though.
calc/disagg:

Updated `disaggregation` calc function doctstring to explain the new equation.
calc/disagg:

Re-worded some of the documentation slightly, for clarity. Also some minor
capitalization and punctuation changes.
tests/calc/disagg_test:

Fixed expected test values for the new disagg equation.
tests/calc/disagg_test:

Updated PMF extractor tests with new results computed by hand/script.
tests/acceptance/disagg_test:

Updated the disagg acceptance test matrix blob to make this "stability"
test pass with the new equation.
calc/disagg:

Corrected disagg calc function to `disaggregation_poissonian`. I kept the old
method so users of the old interface don't blow up. The old function
`disaggregation` will still work, but it will throw deprecation warnings.

Note that the disagg equation has changed, so results are going to be
different anyway.
tests/acceptance/disagg_test:

Updated test to use the new disaggregation interface.
tests/calc/disagg_test:

Updated tests to use the new disaggregation interface.
Merge pull request #102 from larsbutler/correct-disagg

Correction to the disaggregation equation

[r=matley] [f=*1116262]