Remove plugin symbol info(), which is replaced by plugin_set_info()
and a new symbol plugin_info. This is so the PluginInfo struct is
zero'd first by Geany, so plugins are still ABI compatible if we
want to add any more fields in the future.
Fail to load a plugin if plugin_info->name is not set.
Remove now unused string.h include from plugindata.h.


git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@2612 ea778897-0a13-0410-b9d1-a72fbfd435f5