Include sanitized stacktrace in JSON error responses

Squashed commit of the following:
commit 9c1bcef97c4659e3be4fbf9434a816e086186842
commit a054a7bae939b4edcac435b2416f58f0d11bc2a1
commit 320dfbe2a62e6fccf9d63c0312b6c62a59f51e1f

BugzID: 11250
Reformat errors to generate pretty JSON responses

BugzID: 11250
Bypass security check when reading _security object

Tender #57
BugzID: 11719 all_dbs no longer pulls from partition map.

The partition map is updated from a changes listener. When new dbs are created an immediate all_dbs call may not reflect the latest state. all_dbs now pulls directly from the shard_db db.
BugzID: 11719 all_dbs no longer pulls from partition map.
Fix userCtx field in _external request object
Use stock CouchDB OAuth handler
Update spec to include accumulator in timeout response

BugzID: 11432
Update skip_message to handle new accumulator
Fix up type specifications
Remove ?debugFmt message interpreted as error by Hudson
Port workaround for COUCHDB-902

BugzID: 11366
Remove incorrect build instructions
Ignore unknown cast messages

This server needs to be bulletproof.

BugzID: 11762
Fix handling of docs that hash on shard boundaries

BugzID: 11762
Send 100 Continue when appropriate

BugzID: 11762
Set IO priority of worker processes

BugzID: 11762
Fail gracefully on _security if database_does_not_exist

Do the same for _revs_limit, although that's a rarely-used resource.

BugzID: 11762
Fix mixup of case/if catchall clause in 705b57e

BugzID: 11762
Include all the extra details in view group _info

BugzID: 11762