FileUtils.moveFile, copyFile and others can throw undocumened IllegalArgumentException

Several of the functions in FileUtils are throwing undocumented IllegalArgumentException such as moveFile, copyFile and other locations. 

If the desire is to maintain backwards compatibility with the 1.4 branch for these functions, then the 2.12 (and 2.13) versions are throwing IllegalArgumentException in cases  where 1.4 is not. In fact, it seems like 1.4 was coded to specifically avoid IllegalArgumentException and throws IOExceptions instead.

There are several different cases where this is possible.  In the most basic, I've attached TestMoveFileIAE, where this can be reproduced by simple running:

mkdir one
java -cp <your_classpath> TestMoveFileIAE one two
Exception in thread "main" java.lang.IllegalArgumentException: Parameter 'srcFile' is not a file: one
        at org.apache.commons.io.FileUtils.requireFile(FileUtils.java:2824)
        at org.apache.commons.io.FileUtils.moveFile(FileUtils.java:2395)
        at org.apache.commons.io.FileUtils.moveFile(FileUtils.java:2374)
        at TestMoveFileIAE.main(TestMoveFileIAE.java:13)

In a less likely scenario (which is how I found this issue because this happened on a production system); If the srcFile is removed at a certain point during moveFile() execution then IllegalArgumentException is throws:

https://github.com/apache/commons-io/blob/master/src/main/java/org/apache/commons/io/FileUtils.java#L2392

2392    public static void moveFile(final File srcFile, final File destFile, final CopyOption... copyOptions) throws IOException {
2393    validateMoveParameters(srcFile, destFile); // checks srcFile.exists()
		/// ==== srcFile deleted here!!!
2394    requireFile(srcFile, "srcFile");           // checks srcFile.isFile() and throws IAE
2395    requireAbsent(destFile, "destFile");
		/// ==== srcFile could also be deleted here 
2396    ... // renameTo or copyFile() which also calls requireCopyFile() and requireFile()

This pattern of calling validateMoveParameters() and requireFile() will throw IllegalArgumentException every when the srcFile is removed between between validateMoveParameters() and requireFile() or requireFileCopy() and requireFile()

Preferably, it would be best if the 2.x versions of FileUtils were backwards compatible with 1.x and IllegalArgumentException would not be thrown, but IOException (or one of its derivatives) would be. IAE is an unchecked exception and can cause unexpected issues.

I would also suggest that unit tests be created to ensure that these functions behave as expected in error conditions.