This fixes issue #2607.
'RequiredModules' is a field in module manifest that can reference other modules using ModuleSpecification format.
The basic version of this format (just module name) was working fine, however, there was a problem when a more detailed version of the format was used (the one that uses module versions or/and GUIDs).
During module import, there is a check for cyclic references through 'RequiredModules' field. The bug was in this check for cyclic references, related to comparison rules for ModuleSpecification objects - as a result, the code was incorrectly reporting 'cyclic reference' error in cases when there was none.
Also, added tests for different ModuleSpecification formats and a test for error when there is actually a cyclic reference.
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