Issue 178 in svnbook: document ephemeral txnprops (new in 1.8) and how hook scripts might use them.

[svnbook at googlecode.com]

Updates:
	Status: Started

Comment #1 on issue 178 by cmpilato: document ephemeral txnprops (new in  
1.8) and how hook scripts might use them.
http://code.google.com/p/svnbook/issues/detail?id=178

Documented the props in r4412.  Still need to add info and examples about  
their utility.