Simplify configuration of trac-svn-hook

[Ryan J Ollos]

Proposed is a minor change, untested so far, to make it easier to configure trac-svn-hook without edit the file, using ​hook script environment configuration.

See TracRepositoryAdmin@45.

contrib/trac-svn-hook

@@ -45 +45 @@
 #         /path/to/trac-svn-hook $REPOS $REV $USER $PROPNAME
 #     fi
 #
-# See also http://svnbook.red-bean.com/en/1.5/svn.reposadmin.create.html#svn.reposadmin.create.hooks
+# See also http://svnbook.red-bean.com/en/1.7/svn.reposadmin.create.html#svn.reposadmin.create.hooks
 #
 #  Platform:: Unix or Cygwin.
 #
@@ -60 +60 @@
 #
 # == Configuration
 #
-# Uncomment and adapt to your local setup:
+# Uncomment and adapt to your local setup. In Subversion 1.8 and later, you
+# can set these variables in a hook script environment configuration rather
+# than editing this file.
 #
-# export TRAC_ENV=/path/to/trac-env:/path/to/another/trac-env
-# export PATH=/path/to/python/bin:$PATH
-# export LD_LIBRARY_PATH=/path/to/python/lib:$LD_LIBRARY_PATH
+# See also http://svnbook.red-bean.com/en/1.8/svn.reposadmin.create.html#svn.reposadmin.hooks.configuration
+#
+# TRAC_ENV=/path/to/trac-env:/path/to/another/trac-env
+# PYTHON_BIN=/path/to/python/bin
+# PYTHON_LIB=/path/to/python/lib
 #
 # -----------------------------------------------------------------------------
 #
@@ -171 +175 @@
 #
 # This is the script itself, you shouldn't need to modify this part.
 
+export PATH=$PYTHON_BIN:$PATH
+export LD_LIBRARY_PATH=$PYTHON_LIB:$LD_LIBRARY_PATH
+
 # -- Command line arguments (cf. usage)
 
 REPOS="$1"