Ensure line endings are consistent in "make tidy"

[matsduf]

This is the same underlying issue as describe in #828, and it suggests a good solution.

However, it would be good if the error is discovered or corrected early, before the PR with PO file update is created. There is a function that tidies that PO files, "make tidy-po" in share/Makefile that the translator can use for translation work.

Let "make tidy-po" make both msgstr and msgid consistent on final line ending. Or warn that there is a discrepancy if the former is not possible.