python schedd.edit should allow multiple changes to a job_spec without an explicit transaction

As a part of our work to deprecate the python-bindings transaction object, we need a schedd.edit method that allows multiple changes to be made within a single transaction without having an transaction created explicitly.

This should give the same capability to python that we have in the condor_qedit tool. A single list of jobid's or job constraint expression to select job, and a set of key/value pairs to describe the changes.

The changes will be passed as a ClassAd, and the jobs will be specified using the same job_spec as the existing schedd.edit method.

This method will throw a python exception if there is already an open connection to the schedd when it is called.