posixfile_nt: '+' should allow read access.
This fixes unexpected I/O error on committing many files
due to cset:8a53b39cd402 (r4902 in crew).
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
verify failed
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
commit failed