* 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-config.h

@@ -36,7 +36,7 @@ struct _MuConfigOptions {
 	gboolean	 quiet;         /* don't give any output */
 	gboolean	 debug;         /* spew out debug info */
 	char		*muhome;        /* the House of Mu */
-	char             *xpath;	/* path to the Xapian dir */
+	char             *xpath;	/* path to the Xapian dir (internal) */
 	gboolean	 version;	/* request mu version */
 	gboolean	 log_stderr;	/* log to stderr (not logfile) */
 	gchar**	         params;	/* parameters (for querying) */
@@ -54,7 +54,9 @@ struct _MuConfigOptions {
 	char		*fields;	/* fields to show in output */	
 	char	        *sortfield;	/* field to sort by (string) */
 	gboolean        descending;	/* sort descending? */
-	unsigned        summary_len;    /* max # of lines of msg in summary */		
+	unsigned        summary_len;    /* max # of lines of msg in summary */
+	char            *bookmark;      /* use bookmark */
+	char            *bmpath;        /* path to bookmark file (internal) */
 	/* output to a maildir with symlinks */
 	char            *linksdir;      /* maildir to output symlinks */
 	gboolean	clearlinks;     /* clear a linksdir before filling */