Ticks on top axis disappear if tick size is too large (when using bbox_inches='tight')

This is a bug in Matplotlib 1.4 - the following script:

```python
import matplotlib.pyplot as plt

fig = plt.figure()
ax = fig.add_subplot(1,1,1)
ax.plot([1,2,3])

for line in ax.xaxis.get_ticklines():
    line.set_markersize(17)

for line in ax.yaxis.get_ticklines():
    line.set_markersize(17)

fig.savefig('ticks.png', bbox_inches='tight')
```

produces the following output when using ``bbox_inches='tight'``:

![ticks](https://cloud.githubusercontent.com/assets/314716/4264156/b005ecc4-3c17-11e4-9c2a-c0bdad25f1fe.png)

When not setting ``bbox_inches='tight'``, the ticks are there:

![ticks](https://cloud.githubusercontent.com/assets/314716/4264157/c2b3a08c-3c17-11e4-820e-7b4970897089.png)

Addendum:  it turns out I noticed this because some of the image tests in my package were failing - however, this only caused an RMS difference of ~2 or so, so the tolerance has to be quite low to catch this!