Only run 'write' validation in Xcode 6.1 + iOS 8.1

An incredibly ugly diff that does one thing:  detect Xcode 6.1
+ iOS 8.1 and branch to run special validation code.  Otherwise
do what we have always done; write the preferences plist.
Chain synchronize call to NSUserDefaults
Remove unnecessary whitespace
Replace #define with static constant

Matches the rest of the constants in the file.