Worklog#1563 - Support of on-line CREATE/DROP INDEX.

Corrected minor problems of the preceding changeset 1.1705.


sql/sql_table.cc:
  Worklog#1563 - Support of on-line CREATE/DROP INDEX.
  Replaced all tabs by a proper number of spaces. In the diff list this looks unaligned sometimes.
  Changed all sprintf to snprintf and checked the return value.
  Fixed key_count<= 0. key_count is unsigned.
  Removed an obsolete comment.