Fix some crashes and deadlocks

[pondy]

Here are some changes to remove compile warnings and fix stability problems. The highlights are:

• Make the frontend check for ERROR_IO_PENDING before waiting for a write to complete. This fixes a hang in the front end went the interperter process dies as just the wrong time.
• Don't crash the interpreter if the stack size is > 100 or we could not determine the name of a script at a certain level in the stack.
• Don't deadlock the interperter if tostring or towatch calls lua_error() while stopped on a breakpoint.

[dushan42]

I know it's been a while but is there any chance you could break the fixes into individual pull requests? I believe the ERROR_IO_PENDING fix is in but the other stuff isn't and is non-trivial to merge at this point. Thanks! -D