Fix scheduling in retryq

1) Next tick delta was being calculated as seconds _before_ now. This
   should be seconds after now.
2) First operation timeout should take into account the actual timeout
   rather than just its start time.

Change-Id: Ia5058fa91be337c95f79f2156925ebb0d4741b84
Always include configuration.h in distribution

The script would previously include only the files which were found in
the 'include' directory. If re-running gensrclist.pl after a successful
build (which is what I often do in my environment) the problem did not
appear as configuration.h already existed. However running from a clean
tree the configuration.h file is never picked up.

The solution here, is to mention it manually :)

Change-Id: If1b99e76c5c5ffc102a83f5e2d864dd5c882da8e
update release notes

Change-Id: I462987585a909a70a7d3ab0ce0e07762e17df719
cmake fixups (gtest_zip_path)

Change-Id: Ida7aa19665e72ec8539d2a02b9a5366901194bd4
Add multi threaded functionality

This commit adds multi-threaded functionality within libcouchbase. It
works by running a specialized event loop in a dedicated thread, and
using locks to wait and submit operations to the library.

This commit also aims for _API_ compatibility with existing code, so
that newer APIs do not need to be used in order to cooperate with
multiple threads. These wrappers of course are a bit CPU intensive but
work quite well for simple code, or for the sake of porting an existing
lcb-wait based application over to the threaded code.

The wrapping is done partly via dedicated functions, and partly via a
Perl script which generates the proper stubs that can masquerade
themselves as normal API functions to the preprocessor.

WIP because of tests. Many more tests. And API sanity

Currently provided:

- I/O plugin for MT
- mt.h header file
- cbc-mtstress to test and stress the multi-threaded functionality

Change-Id: I783b74bf04f3b818d59610a18bea4435994012c6