Fixes error when modifiying columns

* Fixes unexpected colum casts when renaming a column
* Fixes error when trying to cast numeric columns
* Raises an error when trying to modify system columns
* Don't try to cast a column to the same type

Column casts from date to anything else still not working.
Fixes unp decompressor error on case insensitive file systems

FileUtils raises an error when trying to rename a file using its original
name.