Fix tesseract building on machines without leptonica

component/tesseract/buildout.cfg

@@ -35,8 +35,12 @@ patches =
 configure-command =
   ./autogen.sh
   ./configure --prefix=${buildout:parts-directory}/${:_buildout_section_name_} --disable-static --datarootdir=${tesseract-share:location}
+
+# tesseract has a non-standard way of testing for leptonica, hence the
+# LIBLEPT_HEADERSDIR entry below:
 environment =
   ACLOCAL_ARGS=-I${libtool:location}/share/aclocal
+  LIBLEPT_HEADERSDIR=${leptonica:location}/include
   CPPFLAGS=-I${leptonica:location}/include
   LDFLAGS =-L${leptonica:location}/lib -Wl,-rpath=${leptonica:location}/lib