refactor downloader common ancestor span/binary search fns#21063

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meowsbits:feat/downloader-refactor

Commits on May 11, 2020

downloader: refactor common ancestor algos and logic
meowsbits
committed
downloader: only attempt common ancestor negotiation if > 0 local head
meowsbits
committed
downloader: attempt span search if <= (+or equal) to maxheaderfetch
meowsbits
committed

Commits on May 27, 2020

downloader: use Go conventional if (remove 'else')

meowsbits
and
holiman
committed
downloader: use absolute value of remote vs. local height
meowsbits
committed

Commits on Jun 24, 2020

downloader: handle light sync case as findAncestor condition
meowsbits
committed