Update our cmake modules, the FindXXX stuff

Remove the need for LibFindMacros.cmake. We ask for 2.8, so we don't
need compatibility goo with 2.6.

Also add a nice STATUS message when a package is found without
pkg-config, such as manually installed or system provided stuff.

Except for the licence header, our FindXXX modules are compliant with
the cmake formating rules.
Uniformize the format for CMakeLists.txt

Also shorten it a bit.
Move tnt_broadcast from client to plugins
Add a README in the plugins directory

Also update the CMakeLists.txt, but don't link it to the main
CMakeLists.txt.
Found two minors tweaks for CMakeLists.txt