Find and download old SDK. Older SDKs are found here.
I have copied the xcode.app directory as Xcode_4.6.3.app.
Now you can test and debug in both xcode versions. You have to run them from the corresponding folders or create shortcuts in your desktop. When building from command line give the parameter as iPhoneOS6.1
instead of iPhoneOS7.0
This worked great for me in Xcode5 and iOS.
Go to into Xcode5's SDK dir. Its usually located at:
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs
Add a symbolic link to the old SDK like this:
sudo ln -s /Applications/Xcode_4.6.3.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk iPhoneOS6.1.sdk
Or more accurately from anywhere in the command line,
sudo ln -s /Applications/Xcode_4.6.3.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk