the ldb tool ignores the `—column_family=` parameter with the `compact` command

[ytrezq]

Took a while to understand why ldb compact always does nothing but after debugging in turns out the column family is never passed to CompactRange. Please fix this !

[anand1976]

@ytrezq Can you share the exact commands used to create the DB and then compact it?

[ajkr]

I tried ./ldb compact --db=./tmp-db/ --column_family=column_family_name_000009, and verified it compacted "column_family_name_000009" and nothing else