#90 commit method should call _makeObsolete internally

[Anonymous]

It seems that it is missing a call of _makeObsolete
method inside the commit of class Transaction. Withou
this we can not use begin method properly.

[Oleg Broytman]

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user_id=4799

You don't need to .begin() transaction after .commit(). Just
do some work and .commit() again. You only need to .begin()
after .rollback().