INNODB-LOG-FILE-SIZE

Lower the limit of max number of user-defined columns inside InnoDB from
1020 to 1017. The limit is imposed by the fact that we store the number
in a 10-bit integer (max 1023 columns). We add 3 system columns, which
lowers the limit to 1023-3=1020. In mlog_parse_index() we add the 3
system columns, even though some of them may already be present, which
in worst case means that we may end up with those 3 system columns added
twice to the dummy table object that mlog_parse_index() creates.

The input to mlog_parse_index() is n_fields, n_uniq and the lengths of the
columns. From this data, mlog_parse_index() cannot deduct how many of the
system columns are present and their positions. Here is an example:

Case 1:

CREATE TABLE t1 (a INT, b INT, c INT)

mlog_open_and_write_index():
index=GEN_CLUST_INDEX, table->n_cols=6, n_fields=6, uniq in tree=1, writing (6, 1)

mlog_open_and_write_index() writing DB_ROW_ID's len=32774
mlog_open_and_write_index() writing DB_TRX_ID's len=32774
mlog_open_and_write_index() writing DB_ROLL_PTR's len=32775
mlog_open_and_write_index() writing a's len=4
mlog_open_and_write_index() writing b's len=4
mlog_open_and_write_index() writing c's len=4

Case 2:

CREATE TABLE t2 (a CHAR(6), b INT, c INT, d INT, PRIMARY KEY(a))

mlog_open_and_write_index():
index=PRIMARY, table->n_cols=7, n_fields=6, uniq in tree=1, writing (6, 1)

mlog_open_and_write_index() writing a's len=32774
mlog_open_and_write_index() writing DB_TRX_ID's len=32774
mlog_open_and_write_index() writing DB_ROLL_PTR's len=32775
mlog_open_and_write_index() writing b's len=4
mlog_open_and_write_index() writing c's len=4
mlog_open_and_write_index() writing d's len=4

So when mlog_parse_index() sees the two numbers (n_fields=6, uniq in tree=1)
and then the six lengths (32774, 32774, 32775, 4, 4, 4) it has now way to
distinguish between the above two cases.

Thus we are stuck with this double-counting of sys columns and the simplest
fix is to lower the limit to 1017 so that the double counting does not
overflow the 10 bit integer.

Reviewed by:	Marko (rb:1606)