r3428: switched to using minimal includes for the auto-generated RPC code.

r3428: switched to using minimal includes for the auto-generated RPC code.

The thing that finally convinced me that minimal includes was worth
pursuing for rpc was a compiler (tcc) that failed to build Samba due
to reaching internal limits of the size of include files. Also the
fact that includes.h.gch was 16MB, which really seems excessive. This
patch brings it back to 12M, which is still too large, but
better. Note that this patch speeds up compile times for both the pch
and non-pch case.

This change also includes the addition iof a "depends()" option in our
IDL files, allowing you to specify that one IDL file depends on
another. This capability was needed for the auto-includes generation.
(This used to be commit b8f5fa8ac8e8725f3d321004f0aedf4246fc6b49)