On 26 Jun 2012, Carlos O'Donell told this:
We need to decide if we want to fix install_root for all the
users that are already expecting it to work.
Given the likely triviality of the fix, is it really worth agonizing
over it? I mean, it's no more than this, isn't it?
diff --git a/config.make.in b/config.make.in
index 65410ab..da8fcbd 100644
--- a/config.make.in
+++ b/config.make.in
@@ -5,7 +5,7 @@ version = @VERSION@
release = @RELEASE@
# Installation prefixes.
-install_root = $(DESTDIR)
+install_root ?= $(DESTDIR)