Fix powershell -c 'throw error'
Fix powershell -c 'throw error'

When executing a single command block, two bugs existed.

1) Exceptions were not reported, instead it core dumped
2) The error code was not set, instead 0 was returned

Fixing 1) required calling `Execute` instead of `ExecuteHelper` as the
latter handles exception through `ReportException`.

Fixing 2) required setting the listener's error code when an exception
was thrown, and resetting it for each command when an interactive
session is running.

jsoref/PowerShell,TravisEz13/PowerShell,daxian-dbw/PowerShell,bmanikm/PowerShell,JamesWTruher/PowerShell-1,KarolKaczmarek/PowerShell,jsoref/PowerShell,kmosher/PowerShell,JamesWTruher/PowerShell-1,bmanikm/PowerShell,bingbing8/PowerShell,kmosher/PowerShell,kmosher/PowerShell,kmosher/PowerShell,JamesWTruher/PowerShell-1,PaulHigin/PowerShell,daxian-dbw/PowerShell,bingbing8/PowerShell,bingbing8/PowerShell,bingbing8/PowerShell,KarolKaczmarek/PowerShell,jsoref/PowerShell,jsoref/PowerShell,kmosher/PowerShell,daxian-dbw/PowerShell,daxian-dbw/PowerShell,bmanikm/PowerShell,bingbing8/PowerShell,TravisEz13/PowerShell,KarolKaczmarek/PowerShell,KarolKaczmarek/PowerShell,jsoref/PowerShell,PaulHigin/PowerShell,JamesWTruher/PowerShell-1,PaulHigin/PowerShell,TravisEz13/PowerShell,KarolKaczmarek/PowerShell,bmanikm/PowerShell,TravisEz13/PowerShell,PaulHigin/PowerShell,bmanikm/PowerShell