[gimp] configure: more explicit error message for gtk-encode-symbolic-svg.

[Jehan <jehanp src gnome org>]

commit 11cee13f62d94eb348182c5cfa17e7f4b3a065df
Author: Jehan <jehan girinstud io>
Date:   Sun Aug 19 18:05:42 2018 +0200

    configure: more explicit error message for gtk-encode-symbolic-svg.
    
    Make it obvious this is a tool searched in PATH (and not for instance a
    lib) from the error message.

 configure.ac | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/configure.ac b/configure.ac
index a9b628b93f..cb7b71081a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1830,7 +1830,8 @@ MIME_TYPES="$MIME_TYPES;image/svg+xml"
 AC_CHECK_PROGS(GTK_ENCODE_SYMBOLIC_SVG, gtk-encode-symbolic-svg, no)
 
 if test "x$GTK_ENCODE_SYMBOLIC_SVG" = xno; then
-  add_deps_error([gtk-encode-symbolic-svg])
+  add_deps_error([gtk-encode-symbolic-svg],
+                 [Could not find gtk-encode-symbolic-svg in your PATH.])
 fi
 
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