ipc:sysv:message-queue:rename to msgtool.c

The source will be compiled as msgtool program,
which will utilize the message-queue APIs to
manipulate the queue and its data.
ipc:sysv:message-queue:msgtool

This program uses message-queue APIs to
manipulate the queue and the data.

ftok()
msgget()
msgsnd()
msgrcv(), peek with E2BIG flag
msgctl(): IPC_STAT, IPC_SET, IPC_RMID

ipcs: see system IPC items