make: modifier to run realpath() on variable?

["Simon J. Gerraty" <sjg%crufty.net@localhost>]

The next version of bmake will have a dependency on realpath()
so I'd like to be able to replace things like:

${.PARSEDIR:C,.*,cd & \&\& 'pwd',:sh}

which is expensive if you have to do it 200k times
with:

${.PASEDIR:tA}

to convert .PARSEDIR to an absolute path.
(if realpath fails, the value is not touched).

'A' (or 'a') for 'A'bsolute - but 'r' (or 'R') for 'realpath' might
work too.  

The patch is trivial - apart from picking a name.


Thoughts?
--sjg