Clarify what RT.pm's documentation is about
Convenient initialization via "use RT -init;"

This allows external code to turn the annoying boilerplate of:

    use RT;
    RT->LoadConfig;
    RT->Init;

into

    use RT -init;

as long as it doesn't do anything funky between loading RT, calling
LoadConfig and calling Init.
Docs: RT->LoadConfig and ->Init need to happen at compile time

Most of the time things will still work without the BEGIN block, but any
plugin that provides a library overlay (such as Ticket_Vendor.pm) won't
correctly load it if the script also contains, continuing the example, a "use
RT::Ticket" line.

This is because use statements are is evaluated at compile-time before
LoadConfig and Init are called, and at that point plugins aren't setup
yet when the core library file looks for overlays to load.
Merge branch '4.0/convenient-rt-init' into 4.0-trunk