openalpr 1.2 (new formula)

Hopefully this formula will get a little simpler once/if my upstream pull
request is accepted:

https://github.com/openalpr/openalpr/pull/55

A notable one-off in this formula is that I couldn't include a "depend_on" for tesseract, as the formula depends on the "--devel" version of tesseract.  See the "caveats" method for more info.
I took a look at cake.rb, but couldn't think of something other than actually passing an image file for the program to process.  I could maybe reference an image online somewhere, but didn't think that would be very reliable. (Piping /dev/null to the program as an image didn't do much other than what --version does.)