#258 1.8 change: Hook script environment variables are now configurable

[Pavel Lyalyakin]

http://subversion.apache.org/docs/release-notes/1.8.html#hooks-env

Beginning with Subversion 1.8, hook script environment variables are configurable. Env variables can be configured per-repository (placed to repository's /conf/hooks-env configuration file) or server-wide using the new hooks-env option for svnserve or using new SVNHooksEnv option for Apache.

[C. Michael Pilato]

I introduced the hooks-env file documentation way back in r4420 and r4422.
I added the SVNHooksEnv description to the httpd directive reference in r5081.
And I added the hooks-env description as part of a new section on svnserve configuration in r5084.