Drafting Postdoc Inquiry Follow-up
Extreme timidity is not the best approach in Academia. You have to take initiative, which sometimes involves some risk.

In this case, there isn't really any risk. The Professor expected to communicate with you at the end of the year; otherwise he would not have told you specifically that he would keep you posted. So do remind him, but make it not-salt-rubbing, e.g.:


  Hello Professor HIS_NAME,
  
  We talked several months ago about post-doc position openings at FACULTY_NAME, and you suggested some might become available at the end of the year, provided funding becomes available. I'm writing to ask whether it is now possible for you to say with more certainty whether a position is available.
  
  Respectfully,
  YOUR_NAME
  
  [Quote his original message here]


... and make sure not to send it right on January 1st; wait another week or so. That's really not rubbing salt on the wounds; at most you are gently touching them :-\