Fix gcc warning

warning: use of assignment suppression and length modifier
together in gnu_scanf format. Additionally added comments
next to each of the sscanf variables because there's a lot
of them to keep track of.
Fix another warning: "_FORTIFY_SOURCE" redefined
Use 64-bit time_t

GLib's struct GTimeVal declares tv_sec as glong (will break around 2038).
Our struct timeval declares tv_sec as time_t...
warning: passing argument 1 of 'ctime' from incompatible pointer type
Taken from:
http://anoncvs.estpak.ee/cgi-bin/cgit/openbsd-ports/tree/sysutils/consolekit/patches/patch-tools_ck-history_c
Fix event->type = CK_LOG_EVENT_SYSTEM_START in history

When the type = CK_LOG_EVENT_SYSTEM_START we can't cast the
event to CkLogSeatSessionAddedEvent. Also
find_first_matching_system_stop_event doesn't care about the
2nd argument so just make it NULL to make it clear we aren't
expecting to pass something of value in.
OpenBSD: VT are only available on i386 and amd64

Patch pulled from:
http://anoncvs.estpak.ee/cgi-bin/cgit/openbsd-ports/tree/sysutils/consolekit/patches/patch-src_ck-vt-monitor_c