Sourceforge logged me out before posting patch 1610412 (which can be closed/rejected now - here is an updated version).
This script generates the list similar to that uploaded in Patch 1457790, but with some differences (improvements?).
It parses journal lists from http://www.ncbi.nlm.nih.gov/entrez/citmatch_help.html#JournalLists and tries to generate a sensible abbreviation mapping. It capitalises the title by incrementally matching title words to the abbreviation (Patch 1457790 OTOH seems to guess about the kinds of words that get capitalised, since it capitalises some words that were not in the abbreviation).
A pre-generated file (314Kb gzip) is available at http://graham.poulter.googlepages.com/j_medline_abbrevs.txt.gz
Converts medline journal list to JabRef abbreviations