Rename function printUsage

Function `printUsage` is defined in `lib/exportqueue.plib` and `lib/importqueue.plib`. It causes fatal error:
```
Fatal error: Cannot redeclare printUsage() (previously declared in /usr/local/share/airt/lib/importqueue.plib:99) in /usr/local/share/airt/lib/exportqueue.plib on line 36
```

Functions must be renamed to not causes redeclare error