Keeping my ports tree in sync with the public pkg repo

[Darren Pilgrim]

Is there a way to determine the ports tree revision used for the current 
public pkg repo?

Like any moderately complex system, I have a mix of stock and custom 
packages.  When I go to update stuff, I'll check out the current ports 
tree and fire off poudrerie to build what I need.  There's a race 
condition: if more than a day or two elapse between when the public pkg 
repo was last refreshed and when I check out the ports tree, there's a 
good chance the version in ports and version of the available package 
don't match.  This is particularly true right now because of all the 
movement from staging and other recent framework changes.

The result is portmaster gives me hell.  I'll go to rebuild, say, perl 
or php using portmaster and it will tell me something I've installed 
from pkgs needs to be updated.  I then go check pkg update and it says 
it's up to date.

There are workarounds, but pkg lock shell games are fragile and I really 
dislike having stock builds of libxml, numerous build tools, vim-lite, 
etc. in my private repos.  If I could check out the same ports tree the 
package building cluster used, I'd avoid the issue entirely.