Support large tables in output

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Generate data (e.g 2.9 million rows)
2. Load into PrettyTable using add_row()
3. Print the table

Example:

table_columns = ['file id', 'parent directory (directory id)', 'file name', 
'type', 'extra info']
display_table = PrettyTable(table_columns)
for file_data in file_query():  # this could also be the db_cursor variant
     display_table.addrow([file_data[0], file_data[1], file_data[2], file_data[3], file_data[4]])

print(display_table)


What is the expected output? What do you see instead?

expect that the table gets displayed
instead, it crashes on a memory compliant as PrettyTable tries to convert 
itself into a one big string


What version of the product are you using? On what operating system?

Linux (Kubuntu 14.10), Python 2.7, prettytable 0.7.2

Please provide any additional information below.

Original issue reported on code.google.com by gpcl...@gmail.com on 15 Dec 2014 at 5:02