Convertion from a floating point number to a string caused a
crash.

During rare circumstances a String object could crash when
it was requested to allocate new memory.
A crash could occcur in Field_double::val_str() because of
a pointer referencing memory inside a String object which was
of unknown size.
And finally, the geometric collection should not accept
arguments which are non geometric.


mysql-test/r/gis.result:
  * Test cases change because we intercept the error behind the
  previous crashes much earlier.
sql/field.cc:
  * It makes no sense to impose a lower limit on the length
  and not setting a upper limit will cause crashes later.
sql/item_geofunc.h:
  * Disallow for binding with field- and item types which
  differ from MYSQL_TYPE_GEOMETRY types.