Decrement clients_requesting_changes in a timely fashion

The previous approach using process_tracker was flawed. If a client
reuses a connection, as is common, the clients_requesting_changes
metric will only be decremented when the connection is terminated,
even if the connection is not requesting changes.
new IOQ api
add missing stat
Fix stat name
Move stats cfg to correct name
Revert "add missing stat" -- Missing for a reason!

This reverts commit 7c28c01f51bd43d2bd8a5ea31eb2af0d6833b891.
Add remaining status code stats
Send application/javascript in JSONP responses

closes COUCHDB-2026
Port 001-load.t etap test suite to eunit
Port 002-icu-driver.t etap test suite to eunit

See setup/0 comment for specific info about loading
couch_icu_driver with eunit.
Port 010-file-basics.t and 011-file-headers.t etap test suites to eunit

Both merged into single suite since they tests single target and shares
common bits.
Port 020-btree-basics.t and 021-btree-reductions.t etap suites to eunit

Both merged into single suite since they tests single target and shares
common bits.
Port 030-doc-from-json.t and 031-doc-to-json.t etap suites to eunit

Both merged into single suite since they tests single target and shares
common bits.
Port 040-util.t etap test suite to eunit
Port 041-uuid.t etap test suite to eunit

Config files are removed in favor of using couch_config API instead.
Port 042-work-queue.t etap test suite to eunit

Etap tests were made in flow style, testing the same things multiple
times without real need. For eunit they are split into small test cases
to focus on testing goals.

Timeout on receive is decreased from 3000 to 100.
Port 043-find-in-binary.t etap test suite to eunit

It been merged into couch_util_tests suite.
Port 050-stream.t etap test suite to eunit
Port 06[0-5]-kt-*.t etap test suites to eunit

All merged into single suite since they're test the same module.
Port 070-couch-db.t etap test suite to eunit

Fix ERL_LIB environment variable setting. Add ?tempdb macros for
unique temporary database name generation.