Clarify includeWatching for fundrawtransaction (Steven Roose)
Pull request description:
Might be sufficient to solve https://github.com/bitcoin/bitcoin/issues/16396, https://github.com/bitcoin/bitcoin/issues/7879 and https://github.com/bitcoin/bitcoin/issues/14405.
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Backport of Core [[https://github.com/bitcoin/bitcoin/pull/16397 | PR16397]]