I sometimes need to move my code somewhere else to back it up for a huge api change. I wish I could use a .old folder for this, but arduino builder still compiles those files.

Example error:
/Arduino/sketchbook/libraries/IRLremote/src/.old/IRLremoteReceive.hpp:141:29: error: 'dataNec' was not declared in this scope

I guess the fix is quite simple, as only hidden folders has to be excluded from compiling/linking.