Bug#974538: libkscreenlocker5: kwin cannot start due to missing libkscreenunlocker5 symbols

[Ben Wagner <bungeman@google.com>]

I tend to use aptitude to update and upgrade and it appears that it
was holding back the kwin-x11 package because apparently to update it
the package kde-style-oxygen-qt5 must be removed. Doing a full upgrade
brings everything up to date and seems to work.

However, it seems that because of the ABI break in libkscreenlocker5
there may need to be more specific dependency requirements (like
libkscreenlocker5 > the version where the ABI changed breaks
kwin-common < the last version to use the missing symbol). Hopefully
such rules would avoid this sort of problem (packages might still get
held back, but conflicting versions wouldn't be installed as a
result).