Document the recommended version of `patch`

Patch versions older than 2.7 will error out when mercurial with renamed (but
unchanged) files. This adds the version recommendation to the installation
docs.

Reviewed at https://reviews.reviewboard.org/r/5990/
Fix the text on the "Manual Updates Required" page.

This page suggests that users restart their server, when it ought to suggest
that they restart their web server.

Fixes bug 3416.

Reviewed at https://reviews.reviewboard.org/r/5991/
Merge branch 'release-2.0.x'