mercurial 3.2.3

This updates the mercurial recipe to 3.2.3, addressing CVE-2014-9390.  See the 3.2.3 release notes: http://mercurial.selenic.com/wiki/WhatsNew#Mercurial_3.2.3_.282014-12-18.29

This is my first time touching a homebrew formula so please let me know if I've made a mistake somewhere.