Ability to specify prefix and suffix for temp files

[mfikes]

Akin to the ability to so in https://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#createTempFile(java.lang.String,%20java.lang.String,%20java.nio.file.attribute.FileAttribute...)

[pyrmont]

If you didn't want a file extension, is it just the empty string (as opposed to nil)?

[mfikes]

@pyrmont That's a good question. I have a patch which will accept nil or "", but I wonder if there is any precedent for that. It would be easy to require non-nil arguments for both.