Windows-compatibility: New function for OS detection

Some Windows-incompatibilities that have crept into the Islandora codebase (additional background can be found here: https://groups.google.com/d/msg/islandora/0MAhLDjbago/9knbOynlyIcJ).

This patch introduces a new function -- one that identifies the server's operating system. Several other [patched] modules will make use of this function, including:
*  Audio Solution Pack
*  Large Image Solution Pack
*  FITS Extractor
*  Islandora OCR