topsStack/FilterAndCoherence.py:
+ add .full suffix to the complex coherence filename only if the multilook number is 1
+ for multilook number as 1, do not run looks sub-module
topsStack/Stack.filter_coherence(): add .full suffix only when azLooks * rgLooks == 1
topsStack/mergeBursts.py: add python3 at the top of script
@falkamelung noted a race condition in #106 due to non-atomic directory
checking followed by os.makedirs. This pattern exists in many places
in the codebase so I went ahead and replaced the rest of them.
The new exist_ok usage should be terser and more idiomatic.