survive invalid .ast files

previously died with Assertion error
fix incorrect propagation of fexpr context

potentially reported errors in a too wide context
decouple CDeclUse from the type system to make it optional
- Changed Busyboxbuilding Test to git file tracking
- Changed Busyboxbuilding Test to git file tracking
- Changed Busyboxbuilding Test to git file tracking
Merge remote-tracking branch 'origin/master'
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"Merge" with alex branch
- Merge with upstream/master: decoupling of CDeclUse
- Conflicts: CDeclUse, CTypeSystem, Frontend
Merge remote-tracking branch 'upstream/master'

Conflicts:
	CTypeChecker/src/main/scala/de/fosd/typechef/typesystem/CDeclUse.scala
	CTypeChecker/src/main/scala/de/fosd/typechef/typesystem/CExprTyping.scala
	CTypeChecker/src/main/scala/de/fosd/typechef/typesystem/CTypeEnv.scala
	Frontend/src/main/scala/de/fosd/typechef/Frontend.scala
added testfile
Merge remote-tracking branch 'origin/master'
- Fixed missing features in stats
implemented functions:
getNextOptFeatures
getNextIdFeatures

They now check for elements which we do not want to look further into for our calculation of the list of next features needed for element duplication. I am basically using a blacklist instead of a much longer whitelist of AST elements.
implemented functions:
getNextOptFeatures
getNextIdFeatures

They now check for elements which we do not want to look further into for our calculation of the list of next features needed for element duplication. I am basically using a blacklist instead of a much longer whitelist of AST elements.
Merge remote-tracking branch 'origin/master'
ReturnStatement transformation should now be fixed

Added containsIfdef function and assertion for testing files

Enumerators inside variable Enums are now renamed

Struct names are now renamed
- Add busybox blacklisted files