manual.texi minor fixes

@item

@code{AUTO_INCREMENT} will not work with negative numbers. The reason

for this is that negative numbers caused problems when wrapping from -1 to 0.

@code{AUTO_INCREMENT} for MyISAM tables is no handled at a lower level and

@code{AUTO_INCREMENT} for MyISAM tables is now handled at a lower level and

is much faster than before. For MyISAM tables old numbers are also not reused

anymore, even if you delete some rows from the table.

* example-Foreign keys::        Using foreign keys

* Searching on two keys::       Searching on Two Keys

* Calculating days::            Calculating Visits Per Day

* example-AUTO_INCREMENT::      Using AUTO_INCREMENT

* example-AUTO_INCREMENT::      Using @code{AUTO_INCREMENT}

@end menu