added byte count limiter for read on MString.

MString.cpp

@@ -278,6 +278,13 @@ namespace coreutils {
 	write(ch);
       return *this;
    }
+
+   MString &MString::read(int fd, int count) {
+      char ch;
+      while(count-- && ::read(fd, &ch, 1)) 	 
+	write(ch);
+      return *this;
+   }
    
    int MString::offset() {
       return cursor - data;