override_subpriority support duplicate TARGETID inputs

[sbailey]

This PR adds support for duplicate TARGETID inputs in override_subpriority, while still using the faster geomask.match function when the inputs are unique. Duplicates can occur in secondary programs when more than one secondary matches a primary. Includes unit tests.

[sbailey]

Secondary run completes with

P=/global/cscratch1/sd/adamyers/ADMsecondary/outdata/1.0.1.dev5024/priminfo-dr9-1.0.1.dev5024/

select_secondary $P $CSCRATCH --scnddir /global/cscratch1/sd/adamyers/ADMsecondary \
--dark-subpriorities /global/cfs/cdirs/desi/target/catalogs/subpriority/fba-version-4.0.0/subpriorities-dark.fits \
--bright-subpriorities /global/cfs/cdirs/desi/target/catalogs/subpriority/fba-version-4.0.0/subpriorities-bright.fits

[coveralls]

Coverage increased (+0.04%) to 58.948% when pulling 0b3a7f5 on secondsubprio into 5c84622 on master.