"help misc" in the shell should include Object.bsonsize, other helpers, and objects like NumberLong.

In 1.5.6 I get this:
> help misc
b = new BinData(subtype,base64str) create a BSON BinData value
b.subtype() the BinData subtype (0..255)
b.length() length of the BinData data in bytes
b.hex() the data as a hex encoded string
b.base64() the data as a base 64 encoded string

b.toString()

There also seems to be an extra linefeed before "b.toString()"