* zassert.h: New header file to declare a quagga-specific assert macro.
* log.c: (_zlog_assert_failed) New function called when assert fails
to log the error and abort.
* zebra.h: Include "zassert.h" instead of <assert.h>.
* regex.c: Include "zassert.h" instead of <assert.h>.
* dict.c: Include "zassert.h" instead of <assert.h>.
