added moveBackToLineStart() method on ZString.

ZString.cpp

@@ -583,6 +583,14 @@ namespace coreutils {
 	  ++line;
       return line;      	   
    }
-   
-   
+
+   void ZString::moveBackToLineStart() {
+      while(cursor != data) {
+	 if(*cursor == '\n')
+	   break;
+	 cursor--;
+      }  
+      return;
+   }
+      
 }

ZString.h

@@ -445,7 +445,14 @@ 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;