Versioning caches in Plasma

[Aleix Pol]

Hi,
I just realized that we're versioning caches. I understand we need to
do that to prevent to have get locked into a format version.
Nevertheless, this creates a leak that's not easy to solve. For
example I have several of these that won't get ever cleaned up:
17M     plasma_theme_default_v5.19.kcache
17M     plasma_theme_default_v5.20.kcache
17M     plasma_theme_default_v5.24.kcache
17M     plasma_theme_default_v5.25.kcache
17M     plasma_theme_default_v5.26.kcache

Would it be possible to just have a fast check and whenever the
version is different we flush the cache and populate it again? It's
quite unlikely that anyone will fly into an older version, and if they
do, then repopulating the cache should be fine.

Aleix