Increase debhelper compatibility level to 8

This is done in debian/compat, the recommended way. The setting is also
dropped from debian/rules. This fixes these two lintian warnings:

debian-rules-sets-DH_COMPAT
package-uses-deprecated-debhelper-compat-version
added .gitignore
added final executable to .gitignore
Merge remote branch 'upstream/ipv6' into ipv6
changelog and man page updates for ip6tset
Bug fix: possible buffer overrun.

After the best chunk is selected, if alignment is request, its size
is rounded down before the allocation is made.  If the requested
allocation size is not a multiple of the alignment size, this
may result is allocation of less space than was requested (buffer
overrun).

This fixes the problem, I think, by rounding the requested allocation
size up to a multiple of the alignment size before selecting
the best chunk.
ip6addr.c(ip6prefix, ip6atos): support compressed "::" notation
configure: add test for byte sex
configure: define __SIZEOF_POINTER__ if compiler does not do so already
ip6trie: new dataset type
Makefile.in: Add 'check' target to run self-test and python-driven tests of btrie.c
use dump_ip6() in rblnsd_ip6tset.c
use btrie instead of ip4trie in rbldnsd_ip4trie.c
rbldnsd_acl.c: Use btrie instead of ip4trie

rbldnsd_util.c: Delete the now unused ip4trie code
rbldnsd_acl.c: support ipv6 addresses in ACLs
Allow zero-length CIDR "wildcard" prefixes in ip4trie and acl datasets
Basic tests for acl and ip4trie datasets
configure: add --enable-asserts option to control setting of NDEBUG

By default, assertion checking is disabled.