Merge branch 'maint'

* maint:
  Better advice on using topic branches for kernel development
  Documentation: update implicit "--no-index" behavior in "git diff"
  Documentation: expand 'git diff' SEE ALSO section
  Documentation: diff can compare blobs
  Documentation: gitrevisions is in section 7
  shell portability: no "export VAR=VAL"
  CodingGuidelines: reword parameter expansion section
  Documentation: update-index: -z applies also to --index-info
  Documentation: No argument of ALLOC_GROW should have side-effects

git-am.sh

@@ -137,7 +137,7 @@ It does not apply to blobs recorded in its index."
     export GITHEAD_$his_tree
     if test -n "$GIT_QUIET"
     then
-	    export GIT_MERGE_VERBOSITY=0
+	    GIT_MERGE_VERBOSITY=0 && export GIT_MERGE_VERBOSITY
     fi
     git-merge-recursive $orig_tree -- HEAD $his_tree || {
 	    git rerere $allow_rerere_autoupdate