Owner of files is who runs gitfs

Type of date is now time_t <- cosmetic

Bug in function gitobj:
   in case of tags, the user.commit was a tag, now it is a commit

Enhancements in function __gitfs:
   the second call to gitobj can be shortened
   no write mode is better ensured at the very end
If a tag does not point to a commit, then the date is taken from the tag
listxattr: less eficient, but more flexible