bpo-2180: Treat line continuation at EOF as a SyntaxError

[asottile]

This makes the parser consistent with the tokenize module (already the case
in pypy).

sample

x = 5\

before

$ python3 t.py
$ python3 -mtokenize t.py
t.py:2:0: error: EOF in multi-line statement

after

$ ./python t.py
  File "t.py", line 3
    x = 5\

         ^
SyntaxError: unexpected EOF while parsing
$ ./python -m tokenize t.py
t.py:2:0: error: EOF in multi-line statement

https://bugs.python.org/issue2180

[miss-islington]

@asottile: Status check is done, and it's a failure ❌ .

[miss-islington]

@asottile: Status check is done, and it's a failure ❌ .

[miss-islington]

@asottile: Status check is done, and it's a failure ❌ .

[miss-islington]

@asottile: Status check is done, and it's a success ✅ .