merge-octopus: Work around environment issue on Windows

For some reason, the environment variables get upper-cased when a
subprocess is launched on Windows. Cope with that.

[PT: fixed typo in the char range noted by junio]

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

git-merge-octopus.sh

@@ -61,6 +61,11 @@ do
 	esac
 
 	eval pretty_name=\${GITHEAD_$SHA1:-$SHA1}
+	if test "$SHA1" = "$pretty_name"
+	then
+		SHA1_UP="$(echo "$SHA1" | tr a-z A-Z)"
+		eval pretty_name=\${GITHEAD_$SHA1_UP:-$pretty_name}
+	fi
 	common=$(git merge-base --all $SHA1 $MRC) ||
 		die "Unable to find common commit with $pretty_name"