Fix the "Installing the Linux Environment" part in the SAP section:
- Remove a para about "troubles" with 4.3-STABLE, this is outdated and confusing.
- Remove the version number of linux_base port.
- Rename "Linux Development" to "Linux Development Environment"
- Add a link to Oracle installation
- make install distclean is a better choice than make package to install a port
- Some rewordings, application tags addition, and other tags and manual page entities fixes.