• Require -std=gnu11 in project config. We always required this, but
previously we were relying on the default GCC flags to do so.
• Fix improper use of va_list on non-Intel architectures.
• JsonrpcOutputStream now properly checks for pending operations before
flushing, so that an error is not incorrectly synthesized.
• Improved error propagation from data streams.
• Correctness fixes for stress tests.
