[fpc-pascal] xmlrpc unit

[Marco van de Voort]

In our previous episode, Graeme Geldenhuys said:
> 
> Maybe adding it as a {$warning This unit is deprecated} will suffice
> for now, until r14767 is merged with 2.4.x. I just tested {$warning
> ...} below the 'unit ...;' line, and indeed it does output a warning
> in the compiler output.

I already added text to the source headers and a "deprecated" modifier to
all constructor.

We also want this to show if people use precompiled units :-)