MSI initialization

Before using any other msi command, use the msiAttach command to initialize the subsystem. This command makes the MSI data available to every Tcl interpreter in a process.

The first invocation within a process returns an empty string. Each subsequent invocation returns an error stating the subsystem is already initialized.

For example:

Input: msiAttach

Input: msiAttach
Output: Error: shared memory region is already attached