export/risk:

Corrected `quantile_value` handling in `export_loss_fraction_xml`.
Merge pull request #1224 from larsbutler/fix-multihazcurve-export

Fix `hazard_curve_multi` export

[r=micheles] [f=*trivial]
Merge pull request #1225 from larsbutler/export-loss-fraction-quantile-fix

Export loss_fraction quantile fix

[r=micheles] [f=*trivial]
bin/openquake:

Added '--export-type' command line option.

Options are 'xml' and 'geojson'.
export/hazard:

Cleaned up export interface to more easily support extension for
multiple export formats.
calcs/hazard/general:

Updated the `export` method to use the new hazard export interface
(which requires the caller to specify an export format).
export/risk:

Cleaned up export interface to more easily support extension for
multiple export formats.

It is also now much more consistent with the hazard export module
and associated interfaces.
calcs/risk/base:

Updated calculator `export` method to use the new risk export
interface.
tests/export/hazard_test:

Factored out export (XML) file validation into the `check_export` util
function.
tests/calcs/risk:

Updated calls to the base risk calc `export` method. The new expected
arguments are now consistent with the hazard calculators. (Instead of
simple a boolean, the type/format of exports must be specified.)
tests/export/risk_test:

Updated/fixed tests to match the new risk export interface.
export/hazard:

Removed unused import.