add functionality to PSVersionTable to include GitCommitID and update tests

test/powershell/PSVersionTable.Tests.ps1

@@ -1,6 +1,6 @@
 Describe "PSVersionTable" {
     It "Should have version table entries" {
-	$PSVersionTable.Count | Should Be 8
+	$PSVersionTable.Count | Should Be 9
     }
 
     It "Should have the right version table entries" {
@@ -12,6 +12,7 @@ Describe "PSVersionTable" {
 	$PSVersionTable.ContainsKey("BuildVersion")              | Should Be True
 	$PSVersionTable.ContainsKey("PSCompatibleVersions")      | Should Be True
 	$PSVersionTable.ContainsKey("PSRemotingProtocolVersion") | Should Be True
+	$PSVersionTable.ContainsKey("GitCommitId")               | Should Be True
 
     }