fix #3910 (typo)

Thanks Kloot! :)
fix compile with threadpool disabled
test if validation test still fails without THREADPOOL
add assertion / fix out of index error
enable threadpool again (-> let validation test fail again)
add test_ThreadPool (fails in ~90% of cases for me)

always works with NUM_THREADS 1
testThreadPool: print stats & add additional check
grouped in functions experience effect on weapon parameters, drastically reducing code duplication and shaved off a couple of magic constants
extended GetUnitWeaponState with new properties, and changed accuracy and sprayAngle to be consistent with other entries which did update with experience
fix ThreadPool UT
fix a failing assert in boost::conditional on exit
*link to Picard facepalm image*
!!! boost.test IS NOT THREADSAFE !!!
spawn the threads when OGL is ready
threadpool: move the removal work to other threads
threadpool ut: make the others safe too
validation slave: fix tests
Merge branch 'develop' of github.com:spring/spring into develop
validation buildslave: fix linking
fix #3911: make Threading::IsSimThread a bit safer vs. wrong type deduction
correct BlurHorizontal/Vertical
Merge remote-tracking branch 'origin/develop' into gmlremove