Just because our public API has a typo doesn't mean that virsh
has to keep the typo.

* tools/virsh.c (VSH_CMD_FLAG_ALIAS): New flag.
(nodedevCmds): Use it.
(cmdHelp): Omit alias commands.
(cmdNodeDeviceDettach): Rename...
(cmdNodeDeviceDetach): ...to this.
* tools/virsh.pod (nodedev-detach): Document it.