cext: fix Windows warning about implicit conversion of 32-bit shift to 64 bit
mercurial/cext/revlog.c(1541) : warning C4334: '<<' : result of 32-bit shift
implicitly converted to 64 bits (was 64-bit shift int ended?)
#if no-windows no-osx
$ mkdir -p xdgconf/hg
$ echo '[ui]' > xdgconf/hg/hgrc
$ echo 'username = foobar' >> xdgconf/hg/hgrc
$ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
$ unset HGRCPATH
$ hg config ui.username 2>/dev/null
foobar
#endif