Disable mp4v2 by default, but still use it for Windows and Mac.

Reason: Official Ubuntu and Debian builds do not use mp4v2 and the mp4v2
version found in the repositories is quite outdated.

CMakeLists.txt

@@ -21,7 +21,7 @@
 project(kid3)
 
 set(WITH_TAGLIB ON CACHE BOOL "build with TagLib")
-set(WITH_MP4V2 ON CACHE BOOL "build with mp4v2")
+set(WITH_MP4V2 OFF CACHE BOOL "build with mp4v2")
 set(WITH_ID3LIB ON CACHE BOOL "build with id3lib")
 set(WITH_VORBIS ON CACHE BOOL "build with Ogg/Vorbis")
 set(WITH_FLAC ON CACHE BOOL "build with FLAC")

macosx/buildkid3.sh

 #!/bin/sh
-cmake -G "Unix Makefiles" -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX= -D WITH_TUNEPIMP=OFF ../kid3
+cmake -G "Unix Makefiles" -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX= -D WITH_TUNEPIMP=OFF -D WITH_MP4V2=ON ../kid3
 make
 cpack

win32/buildkid3.bat

@@ -3,6 +3,6 @@
 set PATH=%QTDIR%\bin;%QTDIR%\..\bin;%QTDIR%\..\mingw\bin;%MSYSDIR%\mingw\bin;C:\WINNT\System32;C:\Windows\System32;%PERLDIR%\bin;%DUMPBINDIR%;%CMAKEDIR%\bin
 set INCLUDE=%MSYSDIR%\local\include
 set LIB=%MSYSDIR%\local\lib
-cmake -G "MinGW Makefiles" -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX= -D WITH_TUNEPIMP=OFF -D WITH_MP4V2=OFF ..\kid3
+cmake -G "MinGW Makefiles" -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX= -D WITH_TUNEPIMP=OFF -D WITH_MP4V2=ON ..\kid3
 mingw32-make
 cpack