Added a check to test for duplicate module names.
Merge branch 'unified-builtins2' into duplicateModule
Renaming IO to K-IO in file io.k
Revert "Renaming IO to K-IO in file io.k"

This reverts commit 922232d91a3153e890fa7e597d9c354b3769850b.
Renaming the correct IO modules.
Merge pull request #671 from kframework/duplicateModule

Added a check to test for duplicate module names.