callFetch header handling refactoring needed

[gashcrumb]

This is a...

[x] Feature request
[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Documentation issue or request

Description

callFetch now has several flags that affect what headers are sent to the server like includeContentType and includeAccept etc. I think we should pull all of those out and instead have the code calling callFetch copy the header object and modify it as needed, for example: