merge in all Jeff Dairiki changes
add python tests to DISTFILES and move it to main dir
inline STATS_FMT in btrie.c
instead of re-implementing assert(), just #undef NDEBUG for TEST build
add forgotten tests.py to Makefile.in
asserts are actually ENabled by default
mention NDEBUG in Makefile.in
prepare 0.997+ipv6 version
Revert "asserts are actually ENabled by default"

This reverts commit 2c6ba857a05d7d61cca3f57919e554f8561f417a.