grab fixes from geoserver-exts
Altering the wording around the arcsde extension by adding a link to the readme file.
Merge pull request #804 from RobertDenis/documentation-arcsde

Documentation: arcsde extension
Merge pull request #802 from travislbrundage/docs-fixes

Fixing incorrect ref links
Java 7 dev environment requirement
fix link
Corrected Basic Extensions