Fix buffer overflow in one of strchar2str tests

Thanks to Hendrik Jaeger (a.k.a. henk).
Make colmgr tests less dependent on environment

Thanks to Hendrik Jaeger (a.k.a. henk).
Merge branch 'fixes-for-tests'

Make tests less dependent on environment.

Thanks to Hendrik Jaeger (a.k.a. henk).
Made calculation of dir size visible in :jobs menu
Don't expose background:add_background_job()

Also move related macro, add some comments and update style a bit.
Introduce background:job_t:type
Introduce BJT_TASK and make size calc unimportant
Move background:add_background_job below last use
Align columns in :jobs menu.
Merge branch 'add-dir-size-calc-to-jobs'

* Make calculation of directory size visible in :jobs menu.
* Align columns in :jobs menu.