there is a new plugin: Backup Copy.
It creates a backup copy of the current file in Geany when it is saved. You can specify the directory where the backup copy is saved and you can configure the automatically added extension in the configure dialog in Geany's plugin manager.
This plugin can be used as a poor man's version control system as it saves previous states of a file which can used later again or used for generating diffs against the current file. Another use case is to set the save path to another partition than the one where the file is saved and then it provides backup functionality.
It requires a recent SVN version of Geany to compile and load, at the time of writing, revision 2604 should be good.
Windows DLL: http://geany-plugins.sourceforge.net/backupcopy/backupcopy-0.1_win32.zip (needs Geany 0.15svn_r2604)
Subversion checkout command: