Merge #11011: [Trivial] Add a comment on the use of prevector in script.
Summary:
PR11011 backport https://github.com/bitcoin/bitcoin/pull/11011/files
08f71c29e [Trivial] Add a comment on the use of prevector in script. (Gregory Maxwell)
Test Plan: make
Reviewers: deadalnix, jasonbcox, Fabien, #bitcoin_abc
Reviewed By: deadalnix, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D3480