Nonlib: Add (some) support for opening sessions readonly.

nonlib/Loggable.C

@@ -44,6 +44,7 @@ using std::max;
 
 
 
+bool Loggable::_readonly = false;
 FILE *Loggable::_fp;
 unsigned int Loggable::_log_id = 0;
 int Loggable::_level = 0;
@@ -116,9 +117,20 @@ Loggable::open ( const char *filename )
     if ( ! ( fp = fopen( filename, "a+" ) ) )
     {
         WARNING( "Could not open log file for writing!" );
-        return false;
+        
+        if ( ! ( fp = fopen( filename, "r" ) ) )
+        {
+            WARNING( "Could not open log file for reading!" );
+            return false;
+        }
+        else
+        {
+            _readonly = true;
+        }
     }
     
+    _readonly = false;
+
     load_unjournaled_state();
 
     if ( newer( "snapshot", filename ) )

nonlib/Loggable.H

@@ -70,6 +70,7 @@ class Loggable
         Log_Entry * unjournaled_state;
     };
 
+    static bool _readonly;
     static FILE *_fp;
     static unsigned int _log_id;
     static int _level;
@@ -142,6 +143,8 @@ private:
 
 public:
     
+    static bool readonly ( void ) { return _readonly; }
+
     static bool replay ( const char *name );
 
     static bool snapshot( FILE * fp );