Multiline Eval broken for local variables after first line

[stephenrauch]

Problem description

As discussed here, using local variables with a multi-line eval does not work for locals not on the first line.

This:

df.eval("""c = a * @x
           d = b * @y""", inplace = True)

fails with:

error: pandas.computation.ops.UndefinedVariableError: local variable 'y' is not defined

NOTE: I will be submitting a PR shortly.

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.5.1.final.0 python-bits: 32 OS: Windows OS-release: 7 machine: AMD64 processor: Intel64 Family 6 Model 69 Stepping 1, GenuineIntel byteorder: little

pandas: 0.19.2
nose: 1.3.7
pip: 8.1.2
setuptools: 18.2
Cython: None
numpy: 1.12.0
dateutil: 2.6.0
pytz: 2016.6.1