types. add xdr_{,u_}int{16,32}_t() functions to convert them.
This is necessary, because things like BPF use the RPC headers to look
at the on-the-wire data, so the headers must accurately represent
what's on the wire, too.
gcc generates slightly better code on all of the architectures I checked.
Also changed xdr_wrapstring to return the return value of xdr_string
directly.
they only take two arguments. Presumably this was done to prevent
problems when users passed xdr_string instead of xdr_wrapstring.
Function prototypes are a better way to fix this "problem".
