2020-07-16 11:51 AEST by Arthur Barrett - checkout with base revision copies (like update -c)

this is sort of related to bug 7472 

checkout.cpp calls rcs_update_fileproc() in update.cpp

this calls update_fileproc() which is where the basrev stuff is where do_update_baserev is used.

do_update_baserev itself is just a 'global int' in update, so I guess we either need to export it, or create a 
function in update.cpp that checkout.cpp can call to 'set' the option.

It'll need testing, but in theory it's pretty easy.