Refactor GlobalInfo
git-svn-id: https://svn.sosy-lab.org/software/cpachecker/branches/909-global-info@43420 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
The following should be assured by this MR:
- GlobalInfo cannot be overwritten before it was cleared.
- GlobalInfo cannot be queried unless the only setter was called before.
- Getters in GlobalInfo require a field to be nonnull.
Closes #909 (closed)