test: use more self descriptive name
Support using existing table as lexicon for normal "INDEX"

Comment content in the following "FULTEXT INDEX" line is the point:

    CREATE TABLE Priorities (
      id INT PRIMARY KEY
    ) DEFAULT CHARSET=utf8
      COLLATE=utf8_bin;

    CREATE TABLE Bugs (
      id INT UNSIGNED PRIMARY KEY,
      priority INT COMMENT 'type "Priorities"',
      INDEX priority_index (priority) COMMENT 'table "Priority"'
    ) DEFAULT CHARSET=utf8;

This generates the following groonga schema:

    table_create  Priorities    TABLE_PAT_KEY Int32
    column_create Priorities id COLUMN_SCALAR Int32

    table_create  Bugs          TABLE_PAT_KEY UInt32
    column_create Bugs id       COLUMN_SCALAR UInt32
    column_create Bugs priority COLUMN_SCALAR Priorities

    column_create Priorities bugs_priority_index COLUMN_INDEX|WITH_POSITION Bugs priority

Index for Bugs.priority is defined in Priorities.