Implement many new functions and some minor cleanups

[olsonse]

I've tested and used these patches for the last 6 or so years based on the earlier code.google.com version. I've now reapplied these patches to the new baseline at github with very few conflicts.

These patches also include two bug fixes for:

• Task.is_done: This patch causes Task.is_done to return the value that is written by DAQmxIsTaskDone, rather than the error code that was returned (which is 0 on success, regardless of whether the task is complete or not).
• CounterInputTask.get_duplicate_count_prevention: This patch similarly fixes the return value to be the value written by DAQmxGetCIDupCountPrevent, rather than the error code that was returned.

These patches add interfaces for:

• Device.get_analog_output_sample_clock_supported (DAQmxGetDevAOSampClkSupported)
• System.connect_terminals (DAQmxConnectTerms)
• System.disconnect_terminals (DAQmxDIsconnectTerms)
• System.tristate_terminal (DAQmxTristateOutputTerm)
• Task.get_sample_timing_type (GetSampTimingType)
• Task.set_sample_timing_type (SetSampTimingType)
• Task.reset_sample_timing_type (ResetSampTimingType)
• Task.get_sample_mode (GetSampQuantSampMode)
• Task.set_sample_mode (SetSampQuantSampMode)
• Task.reset_sample_mode (ResetSampQuantSampMode)
• Task.get_samples_per_channel (GetSampQuantSampPerChan)
• Task.get_samples_per_channel (SetSampQuantSampPerChan)
• Task.reset_samples_per_channel (ResetSampQuantSampPerChan)
• Various routines for Getting/Setting physical channel attributes

Other changes in these patches:

• Task.clear Make it called more like the other various DAQmx functions.
• Adds a few more header files for more versions of DAQmx lib

[olsonse]

This patch set has been updated, following @pearu's suggestion that the various items in load_maps be moved to instance variables. As such, _load_maps was removed and this work is now done in the Task constructor.

[olsonse]

Just pushed into this PR a few cherry-picks from @fgoettfert that are definitely applicable to a pre-py3 branch.