fix for platform inconsistency in creation time

this introduces a new field to the filestat struct which accounts for platform differences in time fields.
https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man2/stat.2.html

If you look at the second struct stipulated (the one that contains birthtime), it mentions that that structure is only defined that way when the macro _DARWIN_FEATURE_64_BIT_INODE is defined. Unless 32 bit systems can have this macro defined?