git-prompt: make long upstream state indicator consistent

Use a pipe as a separator before long upstream state indicator. This is
consistent with long state indicators for sparse and in-progress
operations (e.g. merge).

For comparison, `__git_ps1` examples without upstream state indicator:
(main)
(main %)
(main *%)
(main|SPARSE)
(main %|SPARSE)
(main *%|SPARSE)
(main|SPARSE|REBASE 1/2)
(main %|SPARSE|REBASE 1/2)

Note that if there are long state indicators, they appear after short
state indicators if there are any, or after the branch name if there are
no short state indicators. Each long state indicator begins with a pipe
(`|`) as a separator.

Before/after examples with long upstream state indicator:
| Before                          | After                           |
| ------------------------------- | ------------------------------- |
| (main u=)                       | (main|u=)                       |
| (main u= origin/main)           | (main|u= origin/main)           |
| (main u+1)                      | (main|u+1)                      |
| (main u+1 origin/main)          | (main|u+1 origin/main)          |
| (main % u=)                     | (main %|u=)                     |
| (main % u= origin/main)         | (main %|u= origin/main)         |
| (main % u+1)                    | (main %|u+1)                    |
| (main % u+1 origin/main)        | (main %|u+1 origin/main)        |
| (main|SPARSE u=)                | (main|SPARSE|u=)                |
| (main|SPARSE u= origin/main)    | (main|SPARSE|u= origin/main)    |
| (main|SPARSE u+1)               | (main|SPARSE|u+1)               |
| (main|SPARSE u+1 origin/main)   | (main|SPARSE|u+1 origin/main)   |
| (main %|SPARSE u=)              | (main %|SPARSE|u=)              |
| (main %|SPARSE u= origin/main)  | (main %|SPARSE|u= origin/main)  |
| (main %|SPARSE u+1)             | (main %|SPARSE|u+1)             |
| (main %|SPARSE u+1 origin/main) | (main %|SPARSE|u+1 origin/main) |

Signed-off-by: Justin Donnelly <justinrdonnelly@gmail.com>
Reviewed-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-prompt.sh

@@ -109,7 +109,7 @@
 __git_printf_supports_v=
 printf -v __git_printf_supports_v -- '%s' yes >/dev/null 2>&1
 
-# stores the divergence from upstream in $p (for short status) or $upstream (for verbose status)
+# stores the divergence from upstream in $p
 # used by GIT_PS1_SHOWUPSTREAM
 __git_ps1_show_upstream ()
 {
@@ -219,13 +219,13 @@ __git_ps1_show_upstream ()
 		"") # no upstream
 			upstream="" ;;
 		"0	0") # equal to upstream
-			upstream=" u=" ;;
+			upstream="|u=" ;;
 		"0	"*) # ahead of upstream
-			upstream=" u+${count#0	}" ;;
+			upstream="|u+${count#0	}" ;;
 		*"	0") # behind upstream
-			upstream=" u-${count%	0}" ;;
+			upstream="|u-${count%	0}" ;;
 		*)	    # diverged from upstream
-			upstream=" u+${count#*	}-${count%	*}" ;;
+			upstream="|u+${count#*	}-${count%	*}" ;;
 		esac
 		if [[ -n "$count" && -n "$name" ]]; then
 			__git_ps1_upstream_name=$(git rev-parse \