The main thing this commit does is fix race conditions between a
dap client's event handler and sending a launch/attach request.
Some adapters would only respond to a starting request after the
client handled an init event, which could never happen because
the client used to start it's handler after it sent a launch request.
This commit also ignores undefined errors instead of crashing. This
allows the client to work with adapters that send custom events.
Finially, I added some more descriptive error messages and change
client's starting request seq from 0 to 1 to be more in line with
the specs.
15d5186399