There is a newer version of gatk. Once can just copy the gatk-1.3.ebuild under gatk-1.4.ebuild but has to change the MYHASH variable. Works for me on ~amd64. BTW, if one wants to install 1.4-19 version then fetching from GIT repo fails. The ebuild should fiddle a bit with the version variable to suport this numbering scheme.
Forgot to mention this URL where is a nice listing of all versions available: ftp://ftp.broadinstitute.org/pub/gsa/GenomeAnalysisTK/
done