Move threadsafe function builder logic into function-specific modules

Only affects initialize_source_control for now, but should help establish the pattern that modules own the logic to build their functions.

Created by  finchie  yesterday at 00:46
TWEUQ64DU5ZXAEG67GQSS7GDEZ2O2JR5352WRVIIUK5J7ZOMO5QAC
Change contents