Removed the now unneeded dependency python-concurrent.futures from debian/control
refactored conditional loss ratio to avoid the use of the Curve class
manage poes == nan
use a much simpler implementation
Merge pull request #48 from gem/refactor-loss-map

refactor ```conditional_loss_ratio``` to avoid usage of the Curve class
scientific:

Check for an invalid loss ratio/CoV configuration and raise an exception if
found.
tests/vulnerability_function_test:

Added a test to exercise the error condition which is raised when a vuln
function has a loss ratio = 0.0 and a corresponding CoV > 0.0.

This case is mathematically impossible, so an explicit error should be raised
here.
scientific:

Correct the implementation of `_evenly_spaced_loss_ratios`.
tests/scientific_test:

Added some tests for openquake.risklib.scientific._evenly_spaced_loss_ratios.
scientific:

Correct constraint checks for loss ratios. A ratio is NOT a probability, and
should not be constrained to [0, 1]. *sigh*
scientific:

Corrected a parameter name in the docstring for
VulnerabilityFunction.loss_ratio_exceedance_matrix.
scientific:

Corrected LREM computation
(`VulnerabilityFunction.loss_ratio_exceedance_matrix`).
tests/vulnerability_function_test:

Actually test the LREM computation.
Merge pull request #49 from larsbutler/fix-vuln-func

Fix vulnerability functions

[r=matley] [f=1160840,1160844]