[balsa] Restore support for $(DESTDIR) installations

[Peter Bloomfield <peterb src gnome org>]

commit 422efc1bcafd1870f4bf7efeed1fe9422fa14a59
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Thu Apr 27 21:49:52 2017 -0400

    Restore support for $(DESTDIR) installations
    
        * images/Makefile.am: restore support for $(DESTDIR) installations

 ChangeLog          |    6 ++++++
 images/Makefile.am |    2 +-
 2 files changed, 7 insertions(+), 1 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 68e67c2..15afd0b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2017-04-27  Peter Bloomfield  <pbloomfield bellsouth net>
 
+       Restore support for $(DESTDIR) installations
+
+       * images/Makefile.am:
+
+2017-04-27  Peter Bloomfield  <pbloomfield bellsouth net>
+
        Restore updating the icon cache, and remove a redundant action
 
        * configure.ac: find the path to gtk-update-icon-cache.
diff --git a/images/Makefile.am b/images/Makefile.am
index 75621e4..2990823 100644
--- a/images/Makefile.am
+++ b/images/Makefile.am
@@ -18,5 +18,5 @@ install-data-hook:
        if test -x "$(GTK_UPDATE_ICON_CACHE)" ; then    \
            $(GTK_UPDATE_ICON_CACHE)                    \
                --ignore-theme-index                    \
-               $(BALSA_DATA_PREFIX) ;                  \
+               $(DESTDIR)$(BALSA_DATA_PREFIX) ;        \
        fi