Constraint violations inserting commands after a screen session or a subshell ends

[GoogleCodeExporter]

So far this has been seen in zsh, but not confirmed in bash.

What steps will reproduce the problem?
1. source the shell code from a new terminal
2. open a screen session or a subshell
3. enter commands and exit the screen session or subshell
4. enter more commands in the original parent shell

What is the expected output? What do you see instead?

I expect all history to be logged.  In practice, I see constraint violations 
inserting commands since the key uses only the command number and session id.  
Since subshells and screen sessions inherit these values, the constraints are 
not exclusive enough.

We should probably also include the shell PID or possibly the command itself

Please use labels and text to provide additional information.

Original issue reported on code.google.com by [email protected] on 30 Sep 2011 at 7:08

[GoogleCodeExporter]

since PID is not already in the commands table, we can use SHLVL instead.  Both 
screen and subshells increment this value, so it should be safe.

Original comment by [email protected] on 30 Sep 2011 at 7:11