bd CPS: new variable CPSIDP

[bdecon]

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New variable that uniquely identifies members of each unique household. Combines with CPSIDP to uniquely identify people in the CPS. Should basically be the CPSID + PULINENO checked for age, sex, and race. The PULINENO does 99% of the work, but occasionally contains errors that are caught by confirming that the person's age, sex, and race are consistent between each pair of monthly data. If the person matches, use the PULINENO, if not, add one to the max PULINENO for the unique household.

[bdecon]

See #75