It is a very big test and as such it takes a lot of time.

Solution is to divide the test in two parts, one for testing increasing
column size and one for decreasing size.

The innodb branch does extended tests (that myisam is not) due to the
$do_pk_tests variabel, that is the reason why the innodb branch takes
longer.

No increase of memory usage in innodb was found when analyzing, (tested
with looping some millions time of create/drop and alter commands)

The memory exhaust discovered in the test is due to mysqltest which
stores the result in memory (result-file) and this was the biggest
result file in the test framework, so by dividing the test into two
parts also cuts the memory usage of mysqltest.