Fix ynh_app_upstream_version : restore ability to read manifest
Fix ynh_app_upstream_version : restore ability to read manifest

The documentation was saying A, the code was doing B, and calling
functions were expecting both A and B (see
ynh_check_app_version_changed). So this commit aims at making
everyone agree, by matching usage.

YunoHost/moulinette-yunohost,YunoHost/moulinette-yunohost,YunoHost/moulinette-yunohost,YunoHost/yunohost,YunoHost/yunohost,YunoHost/yunohost,YunoHost/yunohost,YunoHost/moulinette-yunohost,YunoHost/moulinette-yunohost