added byte count limiter for read on MString.

MString.cpp

@@ -279,6 +279,13 @@ namespace coreutils {
       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;
    }

MString.h

@@ -231,6 +231,7 @@ namespace coreutils {
       ///
 
       MString &read(int fd);
+      MString &read(int fd, int len);
       
       ///
       ///