Fix ExternalData pre-commit hook on msysGit

The "mv" command on msysGit does not have the "-n" option.
Since the file names involved are computed from their content,
replacing a file is unlikely to change it.

Change-Id: Ia74d0dc5b9870a51b7bc460cc4dbeaa6ba023348
Merge topic 'fix-ExternalData-hook-on-msysGit' into master

b55c8ebf Fix ExternalData pre-commit hook on msysGit