Added a way to specify the render size for EPS files.

There is now a scale parameter that you can pass in to the EpsImageFile.load() function. This parameter is used to specify at what scale Ghostscript renders the EPS internally. Scale needs to be an integer, and all of the internal structures (image size and bounding box) are scaled based on that parameter.
Test harness for EPS files.

We now have a test harness for EPS files. Two variants were created one for the default scale=1 and one where scale=2. These two tests are run against two different EPS files, one with zero for the start of the bounding box and one where this is not the case. PNG test renders are used to make sure the output match what we expect. Lastly the sample EPS files were generated using the included create_eps.gnuplot file and the gnuplot program on a Mac.
Added documentation for the newly added scale argument to EPS’s load() function.
Changed the Ghostscript() function inside of EpsImagePlugin to use subprocess.Popen() instead of the deprecated os.popen().
Added ghostscript dependency.

Travis needs a list of packages to install and we need the ghostscript package to successfully run our EPS test suite.
Loosened testing rigor for EPS files.

Due to differences in rendering between platforms (mainly antialiasing), we had to lower the rigor with which we test our EPS handling. Instead of making the test fail if the rendered image does not exactly match, we now only fail if the images are grossly divergent.
Copy paste issue on that last commit.
Another typo.
We need to write bytes not strings.

Python3 compatibility issue, we need to write bytes to buffers and pipes, not strings. This should still work in python2.6+.
More python3 fixes.

Changed the way the translate command that is passed to ghostscript is generated. This should now work on both python2.6+ and python3.
Merge pull request #412 from MentalPower/master

Added a way to specify the render size for EPS files.