Mark echld and tfshark as experimental in the ./configure help.

Move them to the end of the list of optional programs.
Make it clear that echld is not built by default.
Change capitalization of tshark and tfshark.

Change-Id: Ib702ed72eb2469968e06a16c73a4009ba4cf68ad
Ping-Bug: 10380
Reviewed-on: https://code.wireshark.org/review/3596
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Petri-Dish: Jeff Morriss <jeff.morriss.ws@gmail.com>
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Jeff Morriss <jeff.morriss.ws@gmail.com>