Fix crowdin PO names mapping

Some translation (pt, zh_CN) were accidentally not updated due to the
use of %two_letters_code%, which could overlap for multiple
translations.  use %locale_with_understore% instead, with custom mapping
to loose the country part where it makes no sense.  Crowdin sure doesn't
make doing the right thing easy...
Deduplicate OS X installed .lproj files

Due to various bugs in scripts, some of the lproj directories were
created in multiple variants for some languages (e.g.  zh_Hans and
zh-Hans, pt and pt_PT).  Clean this up, make sure there's only one lproj
per language.  Change copy-translations.sh to use the correct form of _
instead of - as the separator.
Update translations from Crowdin
Check updates downloaded from Crowdin for errors

Add msgfmt error checking to scripts/update-translations-from-crowdin.sh
because Crowdin, weirdly, doesn't check not even the basics.
Increase version to 1.6.19, update NEWS