added moveBackToLineStart() method on ZString.

ZString.cpp

@@ -584,5 +584,13 @@ namespace coreutils {
       return line;      	   
    }
 
+   void ZString::moveBackToLineStart() {
+      while(cursor != data) {
+	 if(*cursor == '\n')
+	   break;
+	 cursor--;
+      }  
+      return;
+   }
       
 }

ZString.h

@@ -446,6 +446,13 @@ namespace coreutils {
 
       int getLineNumberAtCursor();
 
+      ///
+      /// Move the cursor to the beginning of a line or to the beginning of
+      /// the ZString.
+      ///
+
+      void moveBackToLineStart();
+            
     protected:
       char *data;
       char *cursor;