Improve linetrack interface

* include/mailutils/locus.h (mu_linetrack_rebase): New proto.
* libmailutils/locus/linetrack.c (mu_linetrack_rebase): New function.
* libmailutils/diag/diag.c (mu_diag_at_locus_range): New function.

@@ -65,6 +65,7 @@ void mu_lrange_debug (struct mu_locus_range const *loc,
 
 int mu_linetrack_create (mu_linetrack_t *ret,
 			   char const *file_name, size_t max_lines);
+int mu_linetrack_rebase (mu_linetrack_t trk, struct mu_locus_point const *pt);
 void mu_linetrack_free (mu_linetrack_t trk);
 void mu_linetrack_destroy (mu_linetrack_t *trk);
 void mu_linetrack_advance (mu_linetrack_t trk,

@@ -29,6 +29,7 @@
 #include <mailutils/errno.h>
 #include <mailutils/stdstream.h>
 #include <mailutils/stream.h>
+#include <mailutils/locus.h>
 
 void
 mu_diag_init ()
@@ -71,6 +72,37 @@ mu_diag_at_locus (int level, struct mu_locus const *loc, const char *fmt, ...)
 }
 
 void
+mu_diag_at_locus_range (int level, struct mu_locus_range const *loc,
+			const char *fmt, ...)
+{
+  va_list ap;
+  struct mu_locus_range old = MU_LOCUS_RANGE_INITIALIZER;
+  int restore = 0;
+  
+  if (loc)
+    {
+      if (mu_stream_ioctl (mu_strerr, MU_IOCTL_LOGSTREAM,
+			   MU_IOCTL_LOGSTREAM_GET_LOCUS_RANGE, &old) == 0)
+	{
+	  mu_stream_ioctl (mu_strerr, MU_IOCTL_LOGSTREAM,
+			     MU_IOCTL_LOGSTREAM_SET_LOCUS_RANGE, (void*) loc);
+	  restore = 1;
+	}
+    }
+
+  va_start (ap, fmt);
+  mu_diag_voutput (level, fmt, ap);
+  va_end (ap);
+
+  if (restore)
+    {
+      mu_stream_ioctl (mu_strerr, MU_IOCTL_LOGSTREAM,
+		       MU_IOCTL_LOGSTREAM_SET_LOCUS_RANGE, &old);
+      mu_locus_range_deinit (&old);
+    }
+}
+
+void
 mu_diag_vprintf (int level, const char *fmt, va_list ap)
 {
   mu_diag_init ();

@@ -28,9 +28,27 @@ struct mu_linetrack
 			    cols[head + n] (0 <= n <= tos). */
 };
 
+static inline unsigned *
+cols_ptr (mu_linetrack_t trk, size_t n)
+{
+  return &trk->cols[(trk->head + n) % trk->max_lines];
+}
+ 
+static inline unsigned *
+cols_tos_ptr (mu_linetrack_t trk)
+{
+  return cols_ptr (trk, trk->tos);
+}
+
+static inline unsigned
+cols_peek (mu_linetrack_t trk, size_t n)
+{
+  return *cols_ptr (trk, n);
+}
+
 int
 mu_linetrack_create (mu_linetrack_t *ret,
-		       char const *file_name, size_t max_lines)
+		     char const *file_name, size_t max_lines)
 {
   int rc;
   struct mu_linetrack *trk;
@@ -65,6 +83,20 @@ mu_linetrack_create (mu_linetrack_t *ret,
   return 0;
 }
 
+int
+mu_linetrack_rebase (mu_linetrack_t trk, struct mu_locus_point const *pt)
+{
+  char const *file_name;
+  int rc = mu_ident_ref (pt->mu_file, &file_name);
+  if (rc)
+    return rc;
+  mu_ident_deref (trk->file_name);
+  trk->file_name = file_name;
+  trk->hline = pt->mu_line;
+  *cols_ptr (trk, 0) = pt->mu_col;
+  return 0;
+}
+  
 void
 mu_linetrack_free (mu_linetrack_t trk)
 {
@@ -87,18 +119,6 @@ mu_linetrack_destroy (mu_linetrack_t *trk)
 }   
 
 static inline unsigned *
-cols_tos_ptr (mu_linetrack_t trk)
-{
-  return &trk->cols[(trk->head + trk->tos) % trk->max_lines];
-}
-
-static inline unsigned
-cols_peek (mu_linetrack_t trk, size_t n)
-{
-  return trk->cols[(trk->head + n) % trk->max_lines];
-}
-
-static inline unsigned *
 push (mu_linetrack_t trk)
 {
   unsigned *ptr;