Set to 0.12 (released in 2009) and required for version check macros.
Anyway we were using defines only present in 0.14 without checking...
AC_SUBST(GDATA_LIBS)
dnl Poppler ********************************************************************
-PKG_CHECK_MODULES(POPPLER, poppler-glib >= 0.4.2, HAVE_POPPLER=yes, HAVE_POPPLER=no)
+PKG_CHECK_MODULES(POPPLER, poppler-glib >= 0.12.0, HAVE_POPPLER=yes, HAVE_POPPLER=no)
AC_SUBST(POPPLER_LIBS)
AC_SUBST(POPPLER_CFLAGS)