- Replaced some tabs with spaces.

Always look for qfits include files and libraries locally first, because /usr/include can contain a qfits that is different from the one in eclipse.

- Fixed filename handling bug.
- Corrected self.filename updating.

NOTE: self.filename is no longer overwritten during a save.  It is only
      update if it does not exist.

vfprintf/vsprintf, because it is undefined after the call.
Apparently, most libc implementations do not change the va_list argument,
making this bug hard to detect.

Added image.iter_stat() and image.iter_stat_opts() to compute image statistics by iteratively rejecting large outliers