title: Problem with WEBP and LENSFUN when installing 'darktable' from source using cmake
body: <p>I'm trying to install darktable from source. To this end,
  I downloaded darktable-2.4.4.tar.xz from <a href="https://github.com/darktable-org/darktable/releases/tag/release-2.4.4" rel="nofollow noreferrer">here</a>. After unpacking I try to build it with</p>
  
  <pre><code>sudo ./build.sh
  </code></pre>
  
  <p>I get the following errors:</p>
  
  <pre><code>(...)
  -- Checking for one of the modules 'libsoup-2.2;libsoup2'
  -- Could NOT find WEBP (missing: WEBP_LIBRARY WEBP_INCLUDE_DIR) (Required is at least version "0.3.0")
  CMake Error at /usr/share/cmake-3.10/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
  Could NOT find LENSFUN (missing: LENSFUN_LIBRARY LENSFUN_INCLUDE_DIR)
  Call Stack (most recent call first):
  /usr/share/cmake-3.10/Modules/FindPackageHandleStandardArgs.cmake:378 (_FPHSA_FAILURE_MESSAGE)
  cmake/modules/FindLensFun.cmake:37 (find_package_handle_standard_args)
  src/CMakeLists.txt:286 (find_package)
  </code></pre>
  
  <p>However, both WEBP and LENSFUN are installed.</p>
  
  <pre><code>sudo apt-get install webp
  
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  webp is already the newest version (0.6.1-2).
  0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
  </code></pre>
  
  <p>LENSFUN was installed from source.</p>
  
  <p>It's worth mentioning build.sh uses cmake.</p>
  
  <p>What can I do to solve these problems?</p>