This commit changes GLib size units policy.  We now prefer SI units and
allow for use of proper IEC units where desired.

g_format_size_for_display() which incorrectly mixed IEC units with SI
suffixes is left unmodified, but has been deprecated.

g_format_size() has been introduced which uses SI units and suffixes.

g_format_size_full() has also been added which takes a flags argument to
allow for use of IEC units (with correct suffixes).  It also allows for
a "long format" output which includes the total number of bytes.  For
example: "238.5 MB (238,472,938 bytes)".