Fixed crash on the new month when there are no creatures that can get double growth. (#1219, possibly #1217)
The list of double growth creatures will be serialized.
Bumped format.
MSVC: silenced that stupid C4275 warning. (senseless when using STL)

git-svn-id: https://vcmi.svn.sourceforge.net/svnroot/vcmi/trunk@3241 4dfc6b2a-8b31-0410-aa91-d6c70e3ac834