Build detour & nettle only once (if needed).
Fix listing of items (un)locked.

Problem was of the form 'sprintf(buffer, "%s…", buffer, …)'.
Revert "Build detour & nettle only once (if needed)." – too soon for this.

This reverts commit 8559f173f1b8d80b5c09fb6122ba83ae7e70df75.
The cmake feature used in this commit was added in cmake 2.8.8.
Unfortunately, travis uses an older version.
Merge branch 'master' into flyyouhigh