Do not load full PyDSTool just for version number
Py3: fix deprecated form of raising exceptions

Warnings generated by `2to3`.
Py3: fix warning about 'map' with multiple arguments

Full `2to3` warning message:
    "cannot convert map(None, ...) with multiple arguments because map() now
    truncates to the shortest sequence"

While here, make 'dssrt.py' compatible with Python 3
Py3: fix '2to3' warning

Warning message:
    "You should use a for loop here"
Py3: 'setup.py' is ready for Python 3.3
Py3: use absolute imports
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