A final touch to make processing of [base_unit] a little more readable...

...(adds a new merge method for configs).

src/config.cpp

@@ -626,6 +626,26 @@ void config::merge_with(const config& c)
 	}
 }
 
+void config::merge_and_keep(const config& c)
+{
+	// Merge not existing attributes first
+	string_map::const_iterator attrib_it, attrib_end = c.values.end();
+	for(attrib_it = c.values.begin(); attrib_it != attrib_end; ++attrib_it) {
+	    if (values[attrib_it->first] == "")
+            values[attrib_it->first] = attrib_it->second;
+	}
+
+	// Now merge unshared tags
+	for(child_map::const_iterator i = c.children.begin(); i != c.children.end(); ++i) {
+		const std::string& tag = i->first;
+		child_map::const_iterator j = children.find(tag);
+		if (j == children.end()) {
+		    for (int count=0; count < i->second.size(); count++)
+                add_child(tag, *i->second[count]);
+		}
+	}
+}
+
 bool config::matches(const config &filter) const
 {
 	// First match values. all values should match.

src/config.hpp

@@ -21,7 +21,7 @@
 #include "global.hpp"
 
 #include <map>
-#include <memory> 
+#include <memory>
 #include <ostream>
 #include <string>
 #include <vector>
@@ -47,7 +47,7 @@ public:
 	config();
 
 	config(const config& cfg);
-	
+
 	// Create a config with an empty child of name 'child'.
 	config(const std::string& child);
 	~config();
@@ -152,6 +152,9 @@ public:
 	//! Merge config 'c' into this config.
 	//! Overwrites this config's values.
 	void merge_with(const config& c);
+	//! Merge config 'c' into this config.
+	//! Keeps this config's values and does not add existing elements.
+    void config::merge_and_keep(const config& c);
 
 	bool matches(const config &filter) const;
 

src/unit_types.cpp

@@ -927,10 +927,7 @@ void unit_type_data::unit_type_map_wrapper::set_config(const config& cfg)
 			config from_cfg = find_config(based_from);
 
             //merge the base_unit config into this one
-            //ugly hack, but couldn't think of anything better for the moment
-            from_cfg.merge_with(**i.first);
-            (**i.first).merge_with(from_cfg);
-
+            (**i.first).merge_and_keep(from_cfg);
             (**i.first).clear_children("base_unit");
             (**i.first)["id"] = id;
 		}