Ensure only one choco process runs at a time

Multiple running choco processes could potentially cause issues. Look for other choco.exes running (that are not a shim) and report that it cannot run if those are running.

This will not handle the cases where choco dll is embedded and/or being used in things like BoxStarter and ChocolateyGUI. But it should limit most issues.

No files, tests, or entry points are named. Start by tracing choco.exe startup and how the application identifies shim processes, then inspect how running processes can be detected and reported. Done means a normal choco process refuses to run when another non-shim choco.exe is active, while the stated embedded-DLL cases remain outside scope.

Written by the indexing model from the issue text.