Test Cases: Add a git-style file-add patch

[nephros]

Test to check whether git-style diffs behave correctly.

Related: #468

[Olf0]

Oh, likely another case of "do not use GitHub's 'review' functionality, because it creates messages invisible for some"!

My review was / is:

tests/patching/add-a-file-git-style/makediff.sh

@@ -0,0 +1,17 @@
#!/bin/sh

@Olf0:
IIRC pushd, popd and dirs are bashisms.
I fail to find them at https://pubs.opengroup.org/onlinepubs/9699919799/utilities/contents.html

busybox-ash in SailfishOS may be configured to support them when Jolla compiles it, have you checked that?

Still I suggest to call #!/bin/bash as interpreter to make things obvious (busybox-ash in SailfishOS is accompanied by a bash-symlink package), if Jolla's busybox-ash configuration supports them and these three shell built-in commands are indeed bashisms.