Public headers may be compiled with different preprocessor
options than compilation units or private headers within a
project. Introduced a macro WSREP_ASSERT() to be mainly used in
public headers. The macro can be enabled by defining
WSREP_LIB_HAVE_DEBUG and is enabled by default for Debug type builds.
The intended purpose for local mode was local storage access without
entering replication hooks. However, the same can be achieved with
high priority mode. Removed replicating mode and use local instead to
denote locally processing clients.
