Working on master and branch_release-1-8 in the same repository

[Neil Jerram]

I find that when switching from master to branch_release-1-8, I
usually need to do a complete rebuild (i.e. make distclean, autogen,
configure, make, make check).  Do others find this too, or is there
something clever I can do to avoid it and still be sure that I'm
getting correct builds?

Thanks,
     Neil