Make .proto import path computation work with virtual protos in the main repository.
Make .proto import path computation work with virtual protos in the main repository.

Also fix grammar.

ejona86/grpc-java,carl-mastrangelo/grpc-java,stanley-cheung/grpc-java,grpc/grpc-java,stanley-cheung/grpc-java,stanley-cheung/grpc-java,grpc/grpc-java,carl-mastrangelo/grpc-java,dapengzhang0/grpc-java,ejona86/grpc-java,grpc/grpc-java,grpc/grpc-java,dapengzhang0/grpc-java,dapengzhang0/grpc-java,ejona86/grpc-java,ejona86/grpc-java,carl-mastrangelo/grpc-java,dapengzhang0/grpc-java,stanley-cheung/grpc-java,carl-mastrangelo/grpc-java