column is increasing when table is recreated with PS/SP":
make use of create_field::char_length more consistent in the code.
Reinit create_field::length from create_field::char_length
for every execution of a prepared statement (actually fixes the 
bug).


mysql-test/r/ps.result:
  Test results fixed (Bug#13134)
mysql-test/t/ps.test:
  A test case for Bug#13134 "Length of VARCHAR() utf8 column is 
  increasing when table is recreated with PS/SP"
sql/field.cc:
  Move initialization of create_field::char_length to the constructor
  of create_field.
sql/field.h:
  Rename chars_length to char_length (to be consistent with
  how this term is used throughout the rest of the code).
sql/sql_parse.cc:
  Initialize char_length in add_field_to_list. This function
  effectively works as another create_field constructor.
sql/sql_table.cc:
  Reinit length from char_length for every field in 
  mysql_prepare_table. This is not needed if we're executing
  a statement for the first time, however, at subsequent executions
  length contains the number of bytes, not characters (as it's expected 
  to).