THRIFT-2631 c_glib: Support service inheritance in clients

Patch: Simon South
THRIFT-2633 remove 'this is a dummy struct' structs from generated erlang

client: erlang
patch: talentdeficit (alisdair sullivan)

removes dummy struct info clauses from generated code and replaces
them with error that matches other undefined structs. adds error
for non-existent functions to function_info/2