Merge Augie's GitClient refactoring.

diff --cc NEWS
index f0910a1cdd2d9bea367defacdca8aad8af5416b4,f0910a1cdd2d9bea367defacdca8aad8af5416b4..0ebb2d734b73c0f89c0328eeede2995766953c30
--- 1/NEWS
--- 2/NEWS
+++ b/NEWS
@@@ -15,6 -15,6 +15,9 @@@
  
    * Add logging utilities and git/HTTP server logging. (Dave Borowitz)
  
++  * The GitClient interface has been cleaned up and instances are now reusable.
++    (Augie Fackler)
++
   TESTS
  
    * Add tests for sorted_tree_items and C implementation. (Dave Borowitz)