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.
`args << "-D CMAKE_MACOSX_RPATH=true"`