Imports binary property lists to XML format

[Sesquipedalian]

This re-implements a (slightly simplified version of) the changes to "Import Binary Property List.tmCommand" that were contained in the now obsolete #2.

With these changes, binary property list files will be presented using Apple's standard XML format, rather than using pretty_print's idiosyncratic variant of the ASCII format.

This is important for the sake of protecting user data. If the user saves the XML representation back to disk, thereby overwriting the binary version, no data will be lost. In contrast, if the user accidentally saves the output from pretty_plist to disk, the property list file will mostly likely be rendered unreadable.

In the unlikely event that plutil is unavailable, the import process falls back to the previous behaviour.