jsre: hide fields with prefix _ when pretty-printing
jsre: hide fields with prefix _ when pretty-printing

This makes web3 internals like _requestManager invisible.

maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum