#713)

For performance reasons, store bucket configuration as shared pointer,
and copy it instead. The SDK can use shared pointer here, as
configuration is readonly, and only access to the pointer have to be
protected by the mutex

FIT performer need it to compile, as it must support both old and new
version of the core

Backport of #720

All code paths must use update_file_logger to ensure thread safety. The
create_file_logger just updated the logger pointer without incrementing
version.

couchbase_cxx_client.pc have to use absolute path for libdir