Fix for pg_update on win32

Based on EnterpriseDB testing, I have applied the attached patch to fix
a pg_upgrade bug on Win32 on 9.1 and 9.2. The problem is that on Win32
you can't stat() a directory with a trailing slash --- this is already
mentioned in our src/port/path.c. The patch removes a lone trailing
slash.

--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +