Clarify the behaviour of `db.dropDatabase` and the `dropDatabase` command

The drop database command and shell helper are both documented as accepting write concern, but reading through the code and testing them seems to disagree with the documentation.

Specifically:

• From the shell code it looks like db.dropDatabase does not allow any parameters. So how does one specify majority write concern through the shell helper?
• Executing the dropDatabase command directly, without passing write concern seems to always result in a w:majority behaviour. In particular, daniel.hatcher performed these repro steps: "3 member replica set, fyncLocked 2 of the members, command hung on primary".

I am filing this ticket to request clarification on the behaviour of the dropDatabase command and shell helper and to have the documentation updated.