The lexer ignores whitespace like this:

         on whitespace      on non-ws   spontaneously
    IN_START --> IN_WHITESPACE --> JSON_SKIP --> IN_START
                    ^    |
                     \__/  on whitespace

This accumulates a whitespace token in state IN_WHITESPACE, only to
throw it away on the transition via JSON_SKIP to the start state.
Wasteful.  Go from IN_START to IN_START on whitespace directly,
dropping the whitespace character.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180831075841.13363-7-armbru@redhat.com>