PROBLEM
-------

This warning message is printed when trx_sys->rseg_history_len is greater than some
arbitrary magic number (2000000). By seeing the reproducing scenario where we keep
a read view open and do a lot of transactions on table which increases the hitsory
length it is entirely possible that trx_sys->rseg_history_len can exceed 2000000.
So this is not a bug due to corruption of history length.The warning message was
just added to test some scenario and not removed.

FIX
---

1.Print this warning message only for debug versions.
2.Modified the warning message with more detailed information.
3.Don't crash even in debug versions.

[#rb 17929 Reviewed by jimmy and satya]