Harcoded bundle identifier to eliminate bundle collision on GNUstep

On GNUstep, $(PRODUCT_BUNDLE_IDENTIFIER) is never resolved. As a result, we end up with multiple bundles using the same CFBundleIdentifier and -[NSBundle initWithPath:] will always return the first bundle that was registered under this identifier.

CoreObjectInfo.plist

@@ -7,7 +7,7 @@
 	<key>CFBundleExecutable</key>
 	<string>${EXECUTABLE_NAME}</string>
 	<key>CFBundleIdentifier</key>
-	<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
+	<string>org.etoile-project.CoreObject</string>
 	<key>CFBundleInfoDictionaryVersion</key>
 	<string>6.0</string>
 	<key>CFBundlePackageType</key>