tesseract: install leptonica with libtiff

When using tesseract with the default install options, and the
"tessedit_write_images true" config option, usage fails with:

    Error in pixWriteStreamTiff: function not present
    Error in pixWrite: pix not written to stream

Installing leptonica with libtiff support fixes this issue.
Can you remove this and instead change `depends_on "libtiff" => :recommended` in `leptonica.rb`? Thanks!