Eval runs all code instead of just current line

[kenny-evitt]

Copied [and formatted] from several comments on LightTable/LightTable#1673:

it's often execute all codes even if I press ctrl+enter at the first line.

Example code:

import win32com.client #press ctrl+enter at this line,an IE instance is generated.
ieapp=win32com.client.Dispatch("InternetExplorer.Application")
ieapp.Visible=True

as above code, when I eval current line by press ctrl+enter at line 1,the second line is also evaled,and an IE applicathion is showed,thus line 2 and line 3 are also executed.