parser, physics, all: BH tree generation speedup, better parsing, misc

Another mixed bag of commits. I removed the Clang warning workarounds for the parser. If something does not parse correctly in the future -- look at the parser type casting. There's only a few options being typecast anyway. I am quite unsure about mallocing the BH trees. I really plan on changing that because really how many octrees would be the limit anyway. But what can you do, I am a C programmer, if I don't think in terms of memory I ain't programming. Besides, I rather like using NULL pointers to see whether the node is external or internal. I might cook something up soon. Other than that I need to fix the thread creation. I could use phys_find_algorithm to get a function pointer and feed that pointer into pthreads and let it roll but it unleashes a barrage of warnings about how this would strip the attributes of the pointer. Silencing warnings is neither the correct nor right thing to do.