Fix setup.py when using relative paths (#821)
Fix setup.py when using relative paths (#821)

* Fixed the relative path logic for setup.py

* Made relative path OS-independent

* Fix for pip

* One more stab at fixing


Former-commit-id: 10a66a86f221e70606585113ea0e81641bac6e67
clab/dynet,shuheik/dynet,xunzhang/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,shuheik/dynet,chunyang-wen/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet,chunyang-wen/dynet,chunyang-wen/dynet,danielhers/dynet,danielhers/dynet,clab/cnn,shuheik/dynet,clab/dynet,clab/dynet,clab/cnn,clab/dynet,clab/dynet,danielhers/dynet,xunzhang/dynet,shuheik/dynet,shuheik/dynet,shuheik/dynet,xunzhang/dynet,xunzhang/dynet,danielhers/dynet,clab/cnn,clab/dynet