pgbench failed when -f option contains a char '@'

Hi, hackers

pgbench use -f filename[@weight] to receive a sql script file with a weight,
but if I create a file contains char'@', like a@2.sql, specify this file without weigth,
pgbench will failed with error:
    pgbench: fatal: invalid weight specification: @2.sql

This action may be unfriendly, because the char '@' is a valid character on Linux
and Windows.

I have created a patch to modify this action. The patch is attached.

Thoughts?

Regards
Shenhao Wang