This contains a copy of libevent-1.4.7-stable for use on Linux and Mac

Rather than use libevent's own build system, we just build a Chrome 
static library using SConscript

Changes from upstream:
1) add linux/config.h from a run of configure on a Linux development box.
2) add SConscript and libevent.gyp
3) quotes.patch is applied to allow libevent to be used without
being installed (alternative is adding crazy -I arguments to the commandline)
4) The directories WIN32-Code and WIN32-Prj are not included
5) add mac/config.h from a run of configure on a Mac.
6) sys-queue-macros.patch is applied to build on systems which are missing a
complete sys/queue.h

SConscript does not include a few files that don't build on Linux:
    devpoll.c, evport.c, kqueue.c

TODO: currently we -I the source directory, which exposes event-config.h, which
is dangerous as this file was generated for Linux and is not entirely correct on
other platforms.