Fix broken boost mirror for BSD and fix http -> https in some links

Summary:
Provided here: https://github.com/Bitcoin-ABC/bitcoin-abc/pull/286
I'm submitting for review since users are currently having issues receiving signup emails.

Test Plan: Read it + try to download source from the sourceforge target

Reviewers: deadalnix, Fabien, #bitcoin_abc, Mengerian

Reviewed By: #bitcoin_abc, Mengerian

Subscribers: Mengerian, teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2175