Fix bug of git shallow cloning and better performance when cloning

[xuzhongping]

Issue: #106

description

• [x] Fix bug of Git shallow cloning is not used when branch is set.
• [x] Better performance when cloning, if the parameter is branch && commit or tag && commit, determine that the commit is located in the single branch of the branch or tag, and then try whether the depth is 1.
• [x] Replace ASCII with UTF8 in commit_from_ls_remote to handle some character encoding errors (such as Chinese).

It should be noted that this will break the caching mechanism (for the old downloaded cache) when using branch when git downloads in the external pod in cocoapods, because I will keep the parameter ‘branch’ after preprocessing options.

If this modification is approved, I would like to go to the cocoapods gem to optimize git's caching strategy.

other

• Looks similar to the purpose of another PR #117 ? Yes, mainly to fix the same problem, but there are some bugs in that PR, I tried to inform the author, but didn't get a follow-up, I think I can provide a more complete fix.
• It looks like this PR does multiple bug fixes, can't they be dealt with individually? Yes, this PR does more than one bug fix, there are actually three, but there are some dependencies between them, and it would be very troublesome to deal with them separately, so I merged them together,and they all come with adequate testing,you can see my intent in the spec file.

[FKREISE]

Can we please get this merged? Currently, for every pod update we have to download over 500 MB of data because our default branch during development is not master.

With this fix we only have to download 15 MB and it's over 30 times faster! cc @dnkoutso