Phonon: install everything inside CMAKE_INSTALL_PREFIX

[Alexander Neundorf]

Hi,

as discussed in Randa, I now committed a change to Phonon so that now by 
default *everything* is installed inside CMAKE_INSTALL_PREFIX, including the 
Qt designer plugins and the mkspecs file.

The commit is here:
http://commits.kde.org/phonon/664035456f0c9dc85b65c893f431b82118c281c0

There is now a cmake option PHONON_INSTALL_QT_EXTENSIONS_INTO_SYSTEM_QT, if 
set to TRUE, the install directories are set to the system Qt directories.

Additionally, it now checks whether the install directories are the same as 
the system Qt directories, and if not, prints a relatively verbose warning 
(please have a look at this message too).

So, please let me know if you still see any issues or whether this is how it 
should be handled.

Alex