Queries should error if no prefix is provided.

Conflicts:
	server/server_query_handlers_test.go
Fixes prefix override.
Fixes prefix in json for queries.

Conflicts:
	server/server_query_handlers_test.go
Fixes query count test.
Fix period based stream flushing. Adds flush-period and flush-threshold URL param support to the streaming endpoints.

Conflicts:
	server/server_event_handlers.go
	server/server_event_handlers_test.go
Fixes event query handler, events_written reference.
Fixes stream flush and adds better stream flush logging.
Merge pull request #179 from Shopify/dupsort_fix_prefix_query

Dupsort: fix prefix queries to support passing as query param or in json
Merge pull request #180 from Shopify/dupsort_stream_flush

Dupsort: fix streaming endpoint flushing and add support for flush-period and flush-threshold URL parameters
Update factorizer mmap size
Merge pull request #181 from Shopify/factorizer_mmap_size

Bump factorizer mmap size
Add key length logging.
Log actual id.
Adds some nil checks in lua distinct method.
Merge pull request #182 from Shopify/fix_lua_distinct_with_nils

Fix lua distinct with nils
Bump factorizer map size.
Bumps mmap size.
Merge pull request #184 from Shopify/bump_mmap_size

Bump mmap size
pprof
Update reference to OverflowPages from gomdb to match their fix.

See https://github.com/szferi/gomdb/commit/7a5e844277864bb3e70620a36860bb8b2e3b3e75#diff-ec78c1a05bbc9b6368a7ac1e41d25ca8