Move pathbias functions into a new file.

Does not compile yet.  This is the "no code changed" diff.
Make circpathbias and circuitbuild compile.

That was the tricky part
Move other #9731 check to start of its functions

At arma's suggestion.  Looks like I missed this one.
Add missing includes for circpathbias.h
Merge remote-tracking branch 'public/bug10063'