Merge branch 'maint-1.6.0' into maint-1.6.1

* maint-1.6.0:
base85: Make the code more obvious instead of explaining the non-obvious
base85: encode_85() does not use the decode table
base85 debug code: Fix length byte calculation
checkout -m: do not try to fall back to --merge from an unborn branch
branch: die explicitly why when calling "git branch [-a|-r] branchname".

diff --cc builtin-branch.c
Simple merge

diff --cc builtin-checkout.c
index b5dd9c07b42e0130384259715730f52bc8c4e6c3,b76cd22776299955d1ff876b5668f2336b4321a2..f32b14838d718907b105bcefd4e015f31aed1403
--- 1/builtin-checkout.c
--- 2/builtin-checkout.c
+++ b/builtin-checkout.c
@@@ -423,10 -292,15 +423,16 @@@ static int merge_working_tree(struct ch
                         */
                        struct tree *result;
                        struct tree *work;
 +                      struct merge_options o;
                        if (!opts->merge)
                                return 1;
-                       parse_commit(old->commit);
+ 
+                       /*
+                        * Without old->commit, the below is the same as
+                        * the two-tree unpack we already tried and failed.
+                        */
+                       if (!old->commit)
+                               return 1;
  
                        /* Do more real merge */