"managing kernel resources" and platform-specific notes

Hi,

We've got some platform-specific notes in the "managing kernel
resources" (17.4.1 on 8.4devel) page.  Since we recently got
platform-specific sections in the installation instructions (15.8), it
seems a good idea to move these notes to the new sections.

Opinions?

--
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.