rpcrt4: Open the endpoint from the caller of RpcServerUseProtseq* instead of the protseq server thread.

This allows errors to be returned to the caller and to create more than 
one connection for an endpoint.

msi: Use disk_prompt from the media_info structure instead of passing an extra parameter to msi_change_media.

secur32: Use a helper function for creating the signature as this simplifies implementing NTLM2 signing a lot.

Based on a patch by Alex Villacís Lasso.

dbghelp: Make dwarf2 parser only report file numbers when at least one compilation unit really has numbers.