* add basic implementation for bookmark support.

basically, add a file named ~/.mu/bookmarks which looks something like
  ----
  [mu]
  testarch=subject:test maildir:/archive
  inbox=maildir:/inbox
  ----

  now, one can do a query, e.g.

    mu find -b testarch

  which is equivalend to

    mu find subject:test maildir:/archive

 if both a bookmark and a 'normal' search expression are specified,
 the will be concatenated.

 bookmarks starting with mu_ are reserved for mu itself.

src/mu-util.c

@@ -194,7 +194,6 @@ mu_util_guess_mu_homedir (void)
 				".mu");
 }
 
-
 gchar*
 mu_util_guess_xapian_dir (const char* muhome)
 {
@@ -208,6 +207,19 @@ mu_util_guess_xapian_dir (const char* muhome)
 	return xdir;
 }
 
+gchar*
+mu_util_guess_bookmark_file (const char* muhome)
+{
+	gchar *homedir, *bmpath;
+
+	homedir = muhome ? g_strdup(muhome) : mu_util_guess_mu_homedir ();
+	bmpath	= g_strdup_printf ("%s%c%s", homedir, G_DIR_SEPARATOR,
+				   MU_BOOKMARK_FILENAME);
+	g_free (homedir);
+
+	return bmpath;
+}
+
 
 gboolean
 mu_util_create_dir_maybe (const gchar *path)