This commits deletes all references and code for back-bdb and back-hdb.
There is some follow up work still necessary to flush out the admin
guide for back-mdb.
Includes all the changes necessary to fix back-asyncmeta issues
discovered during on-site testing since the start of 2016.
These include:
Issues with stability - crashes and assetion failures
Incorrect behavior during unstable network conditions, such as inability to reset connections
or process responses, or "hanging" to wait for a response that would never be received.
Memory leaks and memory management fixes - major redesign of the way back-asyncmeta
works with memory contexts.
Rewrite was replaced with suffix-massage in configuration, and the network-timeout value was changed to milliseconds.
Incorrect behavior when SASL is used to bind to a target.
Many problems caused by race conditions
Fixes for compiler warnings, and tests.
Cleanup of unused code.
