Trim each backpack part before processing.

Adds additional white-space forgiveness for the custom back config entries.

src/main/java/forestry/plugins/PluginStorage.java

@@ -567,6 +567,7 @@ public class PluginStorage extends ForestryPlugin implements IOreDictionaryHandl
 		String[] parts = list.split("(\\s*;\\s*)+");
 
 		for (String part : parts) {
+			part = part.trim();
 			if (part.isEmpty()) {
 				continue;
 			}