[icedtea-web][rfc] Fix of backup of deployment.properties on some OSs

[Jacob Wisor]

Hello!

Some OSs (e.g. Windows) or file systems do not allow to overwrite while renaming or moving files. It could also depend on the implementation of java.io.File.renameTo(java.io.File), as its specification leaves open the exact semantics.

Although the proposed fix is not really elegant, it should work on the majority of systems. Maybe the whole idea of renaming deployment.properties to always have a safe backup is just redundant on modern operating and file systems, since most of them feature journaled or transactional file systems, so there should always be a safe copy having integrity available.

Happy reviewing!
Jacob