Require minimum args to bitmap operations through explicit check inst…

[alanbernstein]

…ead of through function signature

[coveralls]

Coverage decreased (-0.3%) to 99.692% when pulling dc58eb8 on alanbernstein:bitmap-op-required-args into 0f97474 on pilosa:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 7b94a13 on alanbernstein:bitmap-op-required-args into 0f97474 on pilosa:master.

[coveralls]

Coverage remained the same at 100.0% when pulling af4cd1b on alanbernstein:bitmap-op-required-args into 0f97474 on pilosa:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 6221fe8 on alanbernstein:bitmap-op-required-args into 3f6ec51 on pilosa:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 6221fe8 on alanbernstein:bitmap-op-required-args into 3f6ec51 on pilosa:master.

[yuce]

This looks good!