Bug#802710: musescore: Embeds Qt5's private headers without putting them in a namespace

[Lisandro Damián Nicanor Pérez Meyer]

Source: musescore
Version: 2.0.2+dfsg-1
Severity: important

Hi! While doing qt5's qtbase's private headers transition we noted that musescore
got into the list of packages that needed a transition [lop] but without
build depending on qtbase5-dev.

[lop] <https://release.debian.org/transitions/html/qtbase-abi-5-5-1.html>

My teammate Dmitry Schanev found out that musescore ships a Qt5 private header:

<http://sources.debian.net/src/musescore/2.0.2%2Bdfsg-1/thirdparty/xmlstream/xmlutils_p.h/>

By building this header without a namespace the symbols that it generates matchs the symbols
of qtbase's private stuff, so unnecesarily being part of transitions like this.

This is easily solvable by putting the headers under a namespace (like musescore3rdparty,
for example) and using them trough it.

Another better solution is to avoid embedding private stuff at all, of course :)

Kinds regards, Lisandro.

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (990, 'unstable'), (500, 'buildd-unstable'), (500, 'testing')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.2.0-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=es_AR.UTF-8, LC_CTYPE=es_AR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)