ENH: get directory property should return an empty variable if it is not set, not just have an error

BUG: When generating the name of the custom rule file the character : should be replaced with an underscore because it might be a non-file-name part of a path.

BUG: fix ITK build with xcode, as long as you build it in little parts, this fixes the headermap problem

BUG: It is possible for the nightly start time to be over 24 hours in the future which requires two days to be subtracted.  Using a while loop to make sure enough days are added or subtracted.  It should never be able to iterate more than twice.

BUG: Fix dependencies of custom commands that are relative paths to files or other custom command outputs.

ENH: Added istream and ostream operators for stl string in KWSys when using old streams that do not provide them.