Thanks to Martin Friebe for finding and submitting a fix for this bug!

A table with maximum number of key segments and maximum length key name
would have a corrupted .frm file, due to an incorrect calculation of the
complete key length.  Now the key length is computed correctly (I hope) :-)

MyISAM would reject a table with the maximum number of keys and the maximum
number of key segments in all keys.  It would allow one less than this total
maximum.  Now MyISAM accepts a table defined with the maximum.  (This is a
very minor issue.)


myisam/mi_open.c:
  change >= to > in a comparison (i.e., error only if key_parts_in_table
  really is greater than MAX_KEY * MAX_KEY_SEG)
mysql-test/r/create.result:
  Add test results for bug #26642 (create index corrupts table definition in .frm)
mysql-test/t/create.test:
  Add test case for bug #26642 (create index corrupts table definition in .frm)
sql/table.cc:
  In create_frm(), fix formula for key_length; it was too small by (keys * 2) bytes