git-blame: Fix commit summary not available

Merged Waqar Ahmed requested to merge work/fix-git-blame into master

This is a follow-up of my previous MR. The previous MR broke the behaviour where we showed commit summary inline. This is now fixed.

To fix this, I had to switch to using git blame -p as the underlying command to get blame info for a file. This I think is better because the p switch is there for machine processing.

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