Fix download link for gitian builds

Rebased-From: 164a45f57a8a7367e67a5e65b9e938844730cd87
Github-Pull: #5471
version 0.9.99 -> 0.10.0

Bump version but keep CLIENT_VERSION_IS_RELEASE at false as this is not
a release yet.
Merge remote-tracking branch 'bitcoin/0.10'