Admin and hook improvements

Test batteries for hooks.
Improve diagnostics for hooks. Keep logs.
Hooks to work best under Subversion 1.8+.
Clean options for hook installation.
Add modified `svnperms.py` in distribution.
Trac 0.12+ changeset added and modified notification.
Trac URL template.
Trac comment edit permission.
svn-hooks: improve installation

Install small and generic hooks.
Custom configuations per repositories, not executables.
Configurable `pre-revprop-change` permissions.
svn-hooks: improve tests and docs

More docs on pre-revprop-change-ok.conf + tests.
Fix tests for pre-commit.