Move custom path of JPEG_ROOT, TIFF_ROOT, etc. before system.

Currently `setup.py` setups path of 
```python
TCL_ROOT = None
JPEG_ROOT = None
ZLIB_ROOT = None
TIFF_ROOT = None
FREETYPE_ROOT = None
LCMS_ROOT = None
```
using system env variables and then this variables from `setup.py`.
This pull fix it. 
`setup.py` at first insert custom variables and then appends system in look up path.