Git commit for tdlib 1.7.9

[webmeister]

Since f7829a4 you require a specific tdlib version. But tdlib itself does not provide a tag or release for version 1.7.9 (or really any version that does not end in 0). See tdlib/td#1718 and tdlib/td#1627 for details on their development flow, that also seems to confuse other people.

Could you therefore please link to the exact Git commit that should be used to get a compatible tdlib?

Based on

In fact, if you want to use the most stable TDLib 1.X.Y, you need to search for the first commit with that version and message "Update/Increase layer to ..." and use the commit just before that.

I'd guess that should be tdlib/td@8fd9d89 for tdlib 1.7.9, but I'd rather not guess ;)

[BenWiederhake]

Personally, I use 7d41d9eaa58a6e0927806283252dc9e74eda5512, hence my PR #133.