Always put a slash between the checksum and path in filebucket URLs
Since absolute paths on Windows do not always start with /, we need to
make sure that there is always a slash between the checksum and the
path, or the drive letter will end up being considered as part of the
checksum.
On systems where absolute paths always start with /, the extra slash
is removed by the parsing done to the constructed URL.
Reviewed-by: Nick Lewis <nick@puppetlabs.com>