Support for passing an HTTP or FTP URL for TEMP_CONFIG_DIR

Uses one of curl, wget or fetch to download the provided URL and then decompresses gzip, bzip2 and xz tarballs. The file is extracted to /tmp and the extracted path is set for TEMP_CONFIG_PATH.

I've managed to test this insofar as running it on a BSD VM, I'll setup and test on a Linux VM this evening.

I'm not quite sure what to do about writing tests for it to make sure it reliably works though.