inspector: TTD hangs node, can't exit

[kfarnung]

Tested using latest xplat commit.

Debug a script that ends in an exception (like #266). Once you hit the exception there's no way to exit. Trying to continue doesn't continue to the exit and Ctrl-C doesn't work either.

[mrkmarron]

When the debugger detaches the TTD loop keeps running (node.cc line 4790). In this loop if there is an unhandled exception the TTD system sets a breakpoint at the line with the exception and tries to re-execute but since the debugger isn't attached it does not stop a at this line and hits the exception again.

We probably want to update the check on line 4797 to check if the debugger is still attached (as well as just being enabled) and exit the loop if it is not.

[kfarnung]

@mrkmarron I took a look in a debugger and we don't appear to be getting stuck in that loop, so I'll have to investigate further.