scip-clang's own Preprocessing.h is not behaving modularly

[Varun Gandhi]

Here is a brief log from when I requested indexing for Preprocessing.cc and Worker.cc

[08:33:42 warning] worker 0  : got request to index /Users/varun/Code/scip-clang/indexer/Preprocessing.h (hash: 17236030743847385863)
[08:34:00 warning] worker 1  : got request to index /Users/varun/Code/scip-clang/indexer/Preprocessing.h (hash: 5566312134784314899)

The hashes should be matching up and the header should only be indexed once.