Later FLTK versions (1.1.x?) split into 2 libraries --

check for libfltk_gl.a and .so.  Can't (?) use AC_CHECK_LIB
since it only has C++ entry points.

src/configure.in

@@ -42,7 +42,8 @@ fi
 
 AC_ARG_WITH(mesa, [  --with-mesa        force the use of Mesa instead of other graphics libs], with_mesa=$withval, with_mesa=maybe)
 
-AC_ARG_WITH(cave, [  --enable-cave      compile for CAVE], with_cave=$enableval, with_cave=no)
+dnl No, to compile for the CAVE you need a lot more than this can do... -slevy
+dnl AC_ARG_WITH(cave, [  --enable-cave      compile for CAVE], with_cave=$enableval, with_cave=no)
 
 dnl ---------------------------------------------------------------------
 dnl             Check for basic X windows stuff
@@ -67,6 +68,10 @@ if test -n "$with_fltk" -a -d "$with_fltk"; then
 	   AC_MSG_ERROR("Could not find FL/Fl.H for the fltk library")
 	fi
 	FLTK_LIB="-L$with_fltk/lib -lfltk"
+	if test -f "$with_fltk/lib/libfltk_gl.a" || \
+	   test -f "$with_fltk/lib/libfltk_gl.so"; then
+		FLTK_LIB="-L$with_fltk/lib -lfltk_gl -lfltk"
+	fi
 else
 	# assume the compile does -L/usr/local/lib (they don't do all....)
 	FLTK_INC=-I/usr/local/include