Changed the definition of PGSQL_LIBS for building Kea with PostgreSQL
backend to use pg_config value for LIBDIR rather than LDFLAGS.  The latter
did not build with PostgreSQL 9.3.4 on OS-X or Centos.

Added OS-X version numbers 10.9.1 and 10.9.2 to the test for setting the value
of bind10_undefined_pthread_behavior.  Without this the death test for
conditional variables fails as the problem introduced in 10.9 is still there
as of 10.9.2.  This is unrelated to PostgreSQL.