Signed-off-by: NStefan Weil <sw@weilnetz.de>

The newer version contains fixes for the pixUnsharpMaskingGray*
functions which are relevant for Tesseract (used in ImageData::PreScale
which calls pixScale).
Signed-off-by: NStefan Weil <sw@weilnetz.de>

* Use container based Ubuntu trusty. This provides a newer gcc version
  by default. CI jobs should now start faster.

* Add caching. Leptonica is now only built once for each platform.

* Get Leptonica tar instead of zip file. It's smaller,
  and there is no need to store it on disk.
Signed-off-by: NStefan Weil <sw@weilnetz.de>

Use the latest version which is available.
Remove also some unneeded whitespace.
Signed-off-by: NStefan Weil <sw@weilnetz.de>

This command fails currently:

wget http://www.cmake.org/files/v3.3/cmake-3.3.1-Linux-x86_64.sh

Obviously cmake.org now redirects to https connections, so we have to
fix the URL. Then there still remains a certificate problem. Adding
--no-check-certificate is a workaround which should be removed later.
Signed-off-by: NStefan Weil <sw@weilnetz.de>

Add Leptonica_BUILD_DIR option for CMake find_package in Config mode. Set correct .so name on Linux.