#5932 Fix warnings related to po

[Jonas Hahnfeld]

Fix warnings related to po

Individual commits:
1) Build lilypond-doc in Documentation/po

This avoids warning messages from langdefs.py which tries to load
that locale domain and is also imported during a 'normal' build
while producing the .texi and .info files in Documentation/.

2) Inline po-* targets into po/

Documentation/po/ has a custom po-update.

http://codereview.appspot.com/551830043

[Anonymous]

Passes make, make check and a full make doc.

[Jonas Hahnfeld]

drop po-changes

http://codereview.appspot.com/551830043

[Anonymous]

Passes make, make check and a full make doc.

[Anonymous]

Patch on countdown for April 30th

[Anonymous]

Patch counted down - please push.

[Jonas Hahnfeld]

pushed to staging as

commit eeea9423b22a3c7cd481fe4f481e56fd15381097
Author:     Jonas Hahnfeld <hahnjo@hahnjo.de>
AuthorDate: Thu Apr 23 16:40:43 2020 +0200
Commit:     Jonas Hahnfeld <hahnjo@hahnjo.de>
CommitDate: Thu Apr 30 12:09:44 2020 +0200

    Issue 5932/2: Inline po-* targets into po/

    Documentation/po/ has a custom po-update. Also drop po-changes, it's
    only spamming the output when running po-update.

commit 8a98c1ddfdda31eac4e43704e72309e558399bef
Author:     Jonas Hahnfeld <hahnjo@hahnjo.de>
AuthorDate: Thu Apr 23 16:10:42 2020 +0200
Commit:     Jonas Hahnfeld <hahnjo@hahnjo.de>
CommitDate: Thu Apr 30 12:09:39 2020 +0200

    Issue 5932/1: Build lilypond-doc in Documentation/po

    This avoids warning messages from langdefs.py which tries to load
    that locale domain and is also imported during a 'normal' build
    while producing the .texi and .info files in Documentation/.