scons test doesn't add include flag for cfitsio

This doesn't work for me:
```
$ scons test
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gcc -o test/test_image.o -c -O3 -Wall -Isrc test/test_image.c
test/test_image.c:7:10: fatal error: 'fitsio.h' file not found
#include <fitsio.h>
         ^
1 error generated.
scons: *** [test/test_image.o] Error 1
scons: building terminated because of errors.
$ pkg-config --cflags cfitsio
-I/opt/local/include 
```