recipe file should be given temporary extension

[vsoch]

If a user decides to make a folder named exactly "Singularity" in their upper level directory of the repo (e.g., see this issue https://github.com/gearslaboratory/gears-singularity/issues/1) and the repo associated, the builder will identify the folder as a recipe during upload to storage and weirdness ensues (the upload continually tries to upload mime type text/plain which is actually a folder). This should be reasonable to add to the 2.5 builder.