build: Allow building with autoconf 2.63

Reduces the dependency on autoconf from 2.64 to 2.63 to ease building
on older platforms. There is only a few macros missing and they can
be provided easily.

A handful of tests needed modification. The difference in quoting
behaviour between 2.63 and later require the m4_define() to be
manually unfolded.

The Debian control file is left untouched on purpose. The decision
whether to adjust the dependency is left to the respective maintainers.

Tested with autoconf 2.63 and 2.69.

Cc: Scott Mann <smann@noironetworks.com>
Cc: Don Kehn <dkehn@noironetworks.com>
Signed-off-by: Thomas Graf <tgraf@noironetworks.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
FAQ: Add an entry for multicast snooping with VLAN

Signed-off-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>