adding column definitions to tables.

dict_mem_table_add_col(): Add the parameter "heap" for temporary memory
allocation.  Allow it and "name" to be NULL.  These parameters are NULL
when creating dummy indexes.

dict_add_col_name(): Remove calls to ut_malloc() and ut_free().

dict_table_get_col_name(): Allow table->col_names to be NULL.

dict_table_add_system_columns(), dict_table_add_to_cache():
Add the parameter "heap".
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Additional changes that had to be merged from branches/zip:

dict_table_add_system_columns(): New function, factored out from
dict_table_add_to_cache().

mlog_parse_index(): Add some consistency checks, and make use of
dict_table_add_system_columns().