[Nepomuk] High mutex contention in Nepomuk2::Resource

[Simeon Bird]

Hi,

I rather took my eye off the ball on this one, and the 4.10.2 tagging
caught up on me unawares.
Vishesh, would it be ok if I merge some portion of this? I posted a
review request here:

https://git.reviewboard.kde.org/r/109747/

Would you prefer to merge all the changes, or just the crash fixes but
not the performance changes?

Thanks,
Simeon