(svn r1980) Check $DESTDIR if $DEST_DIR was not set.

Makefile

@@ -98,6 +98,7 @@
 # 		ordinary users, currently it is only used for the debian
 # 		packaging. This value should only be set when calling `make
 # 		install' and is not saved in Makefile.config
+#               (Note that DESTDIR is checked if DEST_DIR is not set.)
 #
 # STATIC: link statically
 # CYGWIN: build in Cygwin environment
@@ -514,6 +515,10 @@ LIBS += -lws2_32 -lwinmm -lgdi32 -ldxguid -lole32 -lstdc++
 TTDLDFLAGS += -Wl,--subsystem,windows
 endif
 
+ifndef DEST_DIR
+DEST_DIR = $(DESTDIR)
+endif
+
 # sets up the paths for use for make install
 ifdef INSTALL
 # We use _PREFIXED vars here, so the paths are recalculated every time, and