Creating a DB with a name containing a colon creates two DBs

steps to reproduce

Type following statements into a mongo shell:

> use D:B
switched to db D:B
> db.c.save({1:1})
> show dbs
D:B     (empty)
D_B     0.03125GB

expected result

One database is created.

actual result

Two databases where created. The one with the colon replaced by underline
has no collections - but a size is shown by show dbs.

The database which is shown empty by show dbs, has collections c and
system.indexes.