gnu: xpdf: Fix detection of freetype.

* gnu/packages/pdf.scm (xpdf)[configure-flags]: Add flag to correctly detect
  freetype. Otherwise, the xpdf binary is not built.

gnu: podofo: Fix detection of freetype.

* gnu/packages/pdf.scm (podofo)[arguments]: Add phase patching the cmake
  file that looks for freetype.

gnu: Add zathura comicbook plugin.

* gnu/packages/pdf.scm (zathura-cb): New variable.

gnu: Add zathura postscript plugin.

* gnu/packages/pdf.scm (zathura-ps): New variable.

gnu: Add zathura DjVu plugin.

* gnu/packages/pdf.scm (zathura-djvu): New variable.

gnu: Add zathura PDF plugin.

* gnu/packages/pdf.scm (zathura-pdf-poppler): New variable.

gnu: Add zathura.

* gnu/packages/pdf.scm (zathura): New variable.
* gnu/packages/patches/zathura-plugindir-environment-variable.patch: New file.
* gnu-system.am: Add it.

Merge branch 'master' into core-updates

gnu: Add Xournal.

* gnu/packages/pdf.scm (xournal): New variable.

gnu: podofo: Add optional input lua.

* gnu/packages/pdf.scm (podofo): Add optional input lua-5.1.

gnu: podofo: Update to 0.9.3.

* gnu/packages/pdf.scm (podofo): Update to 0.9.3.

gnu: podofo: Enable building a shared library.

* gnu/packages/pdf.scm (podofo): Enable building a shared library in addition
    to a static one.

gnu: openjpeg: Upgrade to 2.1.0.

* gnu/packages/image.scm (openjpeg): Upgrade to 2.1.0.
  (openjpeg-2.0): New variable.
* gnu/packages/pdf.scm (mupdf)[inputs]: Use openjpeg-2.0.

Merge branch 'master' into core-updates

gnu: Add QPDF.

* gnu/packages/pdf.scm (qpdf): New variable.

Merge branch 'master' into core-updates

gnu: poppler: build with openjpeg and lcms

* gnu/packages/pdf.scm (poppler): build poppler with openjpeg 1.5 and lcms.

Merge branch 'master' into core-updates

Merge branch 'xorg-updates'

gnu: poppler: Update to 0.28.1.

* gnu/packages/pdf.scm (poppler): Update to 0.28.1.  Use the .xz source
  tarball.