Add Digikam

[tlvince]

Are you interested in adding Digikam to this tap?

I've collated existing efforts (see my notes) and am mostly there in tlvince:digikam, but am currently stumped on the following build error:

-- PKGCONFIG() indicates that libkexiv2 is not installed (install the package which contains libkexiv2.pc if you want to support this feature)
CMake Error at cmake/modules/FindKexiv2.cmake:111 (message):
  Could NOT find libkexiv2 header files
Call Stack (most recent call first):
  extra/kipi-plugins/CMakeLists.txt:126 (FIND_PACKAGE)

[adymo]

I'm open to adding more software to this tap as long as somebody uses it and will maintain the formula. I like and use Digikam on Linux. Same for Okular and Gwenview.

[adymo]

The build error probably happens because superenv doesn't set PKG_CONFIG_PATH for libkexiv2. The library is installed directly to /usr/local and superenv doesn't search that. It looks for .pc files in /usr/loca/opt/libkexiv2/lib/pkgconfig. See Library/Homebrew/extend/ENV/super.rb#148