Remove state dependency from exception handling

[zherczeg]

No description provided.

[zherczeg]

This is a bigger rework of exception handling. The problem is, that now caught exceptions can be re-thrown any number of times, storing the backtrace as part of the exception is not correct. Instead, the program counter is saved into the state in the few cases which matters from exception handling: calls and throws. Traps cannot be caught, so they don't need backtrace. There are other ways to do this. E.g. cloning the exception for each throw, and update its stack trace.