Q:

Obtain git hook event information

In a git hook, environment variables are set to provide the event information that fired the hook.  Accessing environment variables for the correct commit information worked fine except when downgraded to git 1.7.1 which do not supply all of the git environment variables. 

A:

The solution was to upgrade git from 1.7.1.  This may seem like a simple oversight and that is correct.  It appears 1.7.1 added functionality in the same way as 1.7.  The second and third place numerical positions apparently did not have a distinct meaning.  For my situation upgrading to 1.7.6 fixed the issue. 
I hope this information is helpful to others writing git-hooks.