Advice on supporting 9.x / 10.x CAM driver

[Chuck Tuffli]

There was a small-ish change in CCB flags and buffer mapping that
occurred between 9-stable and 10 that at first glance prevents a 9.x
driver from compiling on a 10.x system. All of which is fine as this
is a major release.

What I'm curious about is have others come up with a strategy to
support their drivers on both 9.x and 10.x? If so, how are you
managing this? Different branches under a VCS? #ifdef macros? Some
sort of compatibility shim? TIA!

--chuck