added sha() def to commit object

grit.gemspec

@@ -1,6 +1,6 @@
 Gem::Specification.new do |s|
   s.name     = "grit"
-  s.version  = "0.9.1"
+  s.version  = "0.9.3"
   s.date     = "2008-04-24"
   s.summary  = "Object model interface to a git repo"
   s.email    = "tom@rubyisawesome.com"

lib/grit/commit.rb

@@ -182,6 +182,10 @@ module Grit
     def to_s
       @id
     end
+
+    def sha
+      @id
+    end
     
     # Pretty object inspection
     def inspect