execute.c: little modernization
test-hashmap: fix access to uninitialized memory
journald: accept EPOLLERR from /dev/kmsg

Also print out unexpected epoll events explictly.
build-sys: add ./configure --enable-address-sanitizer

Enabling address sanitizer seems like a useful thing, but is quite
tricky. Proper flags have to be passed to CPPFLAGS, CFLAGS and
LDFLAGS, but passing them on the commandline doesn't work because
we tests are done with ld directly, and not with libtool like in
real linking. We might want to fix this, but let's add a handy
way to enable address checking anyway.
Move functions around to fix underlinking in test-machine-tables
Move part of logind.c into a separate file

liblogind-core.la was underlinked, missing a few functions
defined in logind.c. They are moved to a new file, logind-core.c,
and this file is linked into liblogind-core.la.
In addition, logind-acl.c is attached to the liblogind-core.la,
instead of systemd-logind directly.