Add code to extract.pl.in to prevent further cli function overwrites

Add code to extract.pl.in to prevent further cli function overwrites

Currently extract.pl.in is used to build the vtysh cli.  When two
different cli's collide with the same command name, the original
cli is never called, because it is dropped.  This code notes the
silent drop and tracks the number of drops.  If they change then
the code will fail the build.  The current number of drops was
figured out by running extract.pl and counting up the drops
then adding code to compare the numbers returned.

If you have added to the problem, the solution is to fix your cli
command to not stomp on someone else's command.  If you have removed
a stomp, safely modify extract.pl.in as part of your commit.

Signed-off-by: Donald Sharp <sharpd at cumulusnetworks.com>
Acked-by: Vincent Jardin <vincent.jardin@6wind.com>