Make replicated commands behave differently during replication

The following commands can fail during replication when they should not; when being applied during replication with "fromRepl" they should behave differently:

• create collection (should check if collection already exists with spec. opts)
• create index (should already work)
• convert to capped (check that the collection is capped)
• drop db (don't error if missing)
• drop collection (don't error if missing)
• drop index (don't error if missing)