VFide: Preprocessing error when including same header via different paths.

[necto]

This is a tricky bug in the current snapshot of VeriFast. Here are the steps to reproduce:
1. create a directory ./tst
2. create files with the following contents.
./tst/tst.c :

#include "tst.h"
#include "tst/tst.h"

and ./tst/tst.h :

#ifndef _GUARD_
#define _GUARD_
#include <stdlib.h>
#endif

Resulting in this directory structure:

└── tst
    ├── tst.c
    └── tst.h

3. Run vfide -I . (Note: do it from the parent directory of tst)
4. Open the tmp/tst.c from inside the IDE (it is important not to supply it directly as vfide -I . tst/tst.c)
5. If you hit the verify button, you should get:

Preprocessing error: Different amount of tokens were consumed by normal and context-free preprocessors

Note: the same example works perfectly with verifast or when you open it directly with vfide -I . tst/tst.c