WL#797: Option to really Wipe data on delete/drop

Some security conserned applications (Goverment etc) require to really ensure
data is really gone as soon as it is deleted, or at least this possibility can
be reached.  

There are several possible ways to implement it

1) option --wipe-data which will force MySQL to wipe deleted rows data as well as 
Tables on deletion.
2) We can add option to the table, something like AUTO_WIPE=1 to enable wiping
data on delete/drop
3) (easier way) we can just offer commands to completely wipe table instead of
simply dropping it as well as similar command to wipe deleted rows from the table.

If we really go for security we also would make sure no extra copies of secure
data is left due to ALTER/OPTIMIZE table, temporary tables or sort files.