bug#8071: Please rename automake invocation node

[Reuben Thomas]

This is actually a bug that affects several autotools packages,
excluding autoconf, for which it's already fixed: the invocation node
is added to the info dir as "automake" which means that

info automake

goes to the invocation node, not the Top node.

autoconf calls its invocation node autoconf-invocation instead.

While on this subject; all the other autotools entitle their
invocation nodes "autofoo Invocation", whereas automake calls its
"Invoking Automake".

Checked against git head.

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