Fixed docstring typos

Begin commit messages with two empty lines. This makes editors like Emacs wrap the commit message correctly. With no empty line between the commit message and the 'HG:' lines, the 'HG:' lines would be wrapped as if they belonged to the commit message and so lose their significance to Mercurial. This makes no difference to what is stored by the commit -- whitespace was already stripped from the beginning and end of commit messages.