Turn off branch change detection as it leads to endless loop and CPU leak

I believe branch change detection is broken for a long time (since 4.0 came
out). For example you change git branch and KDevelop starts rebuilding
syntax. Looks OK. But, it looses most symbols in opened files forever: they
become dark and non-jumpable. Reloading file or force rebuild syntax tree
doesn't help. When you close KDevelop it goes into endless loop. So after
killing it with -9 and restarting it the symbols become jumpable again. I
don't remember exactly, but KDevelop can go into endless loop without close
action.

These manipulations with kill and restart are required after every branch
change which happen quite frequently. So please, add an ability to turn off
branch change detection.

-- 
All the best,

Aleksey Midenkov
@midenok