GroovyMain command line switch -i fails when no backup extension is specified

The command

groovy -pi -e "(line =~ 'a').replaceAll('b')" ok.txt

fails with

Caught: java.io.IOException: unable to rename ok.txt to C:\DOCUME~1\TOMWHI~1\LOC
ALS~1\Temp\groovy_61377.tmp

whereas

groovy -pi.bak -e "(line =~ 'a').replaceAll('b')" ok.txt

works fine.

The problem is that after creating a temporary backup file using File.createTempFile() the code needs to delete it before renaming the original to the backup.

The attached patch file fixes the problem.