Correct reference guide description of cursor reset in transactions

Summary

The Cursor operations page in the reference guide says:

Cursor positions do not survive transactions: cursors that are open during WT_SESSION::begin_transaction, WT_SESSION::commit_transaction or WT_SESSION::rollback_transaction will lose their position as if WT_CURSOR::reset was called.

This is incorrect.  In the code, we reset cursors in WT_SESSION::rollback_transaction and in when WT_SESSION::commit_transaction fails. Successful calls to WT_SESSION::begin_transaction and WT_SESSION::commit_transaction leave a session's cursors positioned.  

We should fix this statement and do a search through the rest of the documentation to see if there are similar statements elsewhere that need to be corrected.