limit produces bad results with Floats

[skirpichev]

An example is sympy/sympy#11270. More simple test:

In [1]: e = log(exp(1/x)/Float(2) + exp(-1/x)/2)*x**2

In [2]: e.limit(x, oo)  # Float(0.5) would be better
Out[2]: ∞

In [3]: e = log(exp(1/x)/2 + exp(-1/x)/2)*x**2

In [4]: e.limit(x, oo)
Out[4]: 1/2

In some sense Out[2] is not wrong:

In [3]: e2 = log(exp(1/x)/(2 + y) + exp(-1/x)/2)*x**2

In [4]: e2.limit(x, oo)
Out[4]: 
      ⎛   ⎛y + 4⎞         ⎞
∞⋅sign⎜log⎜─────⎟ - log(2)⎟
      ⎝   ⎝y + 2⎠         ⎠