Minc_modify_header allows the modification, insertion or
deletion of attributes in a minc file. If possible, the file is
modified in place, without copying the data. This will happen when
inserting (modifying) an attribute that already exists and that ends
up being the same length or shorter in the new file. If an attribute
is deleted or lengthened, then a complete copy of the data is made,
resulting in a completely new file that replaces the original.
If the file is compressed, then it is first decompressed into a file
whose name is either the same as that of the original file up to the
".mnc" extension or the same minus the compression extension
(".bz", ".bz2", ".gz", ".Z", ".z" or ".zip").
The new file will not be re-compressed.
Care is taken to completely overwrite any existing attribute when
inserting a new attribute so that information is guaranteed to be
removed from the file.