Fix temporary folder name generation collisions

First, the regular expression matches everything after the first period
in a filename.  Adding the $ make it match the last, so that filenames
such as “Report.1.pdf” get trimmed to “Report.1”.

Next use mktemp to get the OS to create a temporary folder.  It will
guarantee a unique directory name beginning with prefix, even if parallel
processes are at work.
Merge pull request #57 from jbarlow83/for-upstream/tmpfolder

Fix temporary folder name generation collisions