The svg2png icon cache is now cleared on new minor version

The `version` value from the `Options` file is compared to the harcoded
value (computed at build time) of the running application. If the major
or minor version is different, the `svg2png` folder is cleaned at
startup-time.

rtgui/options.h

@@ -426,6 +426,7 @@ public:
     Glib::ustring findProfilePath (Glib::ustring &profName);
     bool is_parse_extention (Glib::ustring fname);
     bool has_retained_extention (const Glib::ustring& fname);
+    bool is_new_version();
     bool is_extention_enabled (const Glib::ustring& ext);
     bool is_defProfRawMissing();
     bool is_bundledDefProfRawMissing();