/*
 * Parse value of the argument to the "filter" keyword.
 * On the command line this looks like:
 *       --filter=<arg>
 * and in the pack protocol as:
 *       "filter" SP <arg>
 *
 * The filter keyword will be used by many commands.
 * See Documentation/rev-list-options.txt for allowed values for <arg>.
 *
 * Capture the given arg as the "filter_spec".  This can be forwarded to
 * subordinate commands when necessary (although it's better to pass it through
 * expand_list_objects_filter_spec() first).  We also "intern" the arg for the
 * convenience of the current command.
 */