Respect the case-sensitivity setting in git's config

[alextegelid]

When I rename a file from filename.php to Filename.php GitGutter will show every row in that file as added (thinking it's a new file). git status, on the other hand, reports a clean working tree since my global settings file says core.ignorecase=true

[deathaxe]

This is actually a bug of git so far. as calling git show Filename.php works case insensitive but git show HEAD:Filename.php does not.