Default second argument to the current branch

If not included.

Means that you can write:

  ./compare master

To compare the current branch to master and not have to list out and
copy and paste the current branch.

documentation/compare

@@ -3,17 +3,23 @@
 first=$1
 second=$2
 
-if [ -z "$second" ]; then
-	echo "Usage: compare <branch name A> <branch name B>"
+if [ -z "$first" ]; then
+	echo "Usage: compare <branch name A> [<branch name B>]"
+	echo ""
+	echo "The second argument defaults to the current branch if not specified"
 	exit 1
 fi
 
-firstdir=comparison/first
-seconddir=comparison/second
-
 # Remember the branch we're on
 currentbranch=`git symbolic-ref --short HEAD`
 
+if [ -z "$second" ]; then
+	second=$currentbranch
+fi
+
+firstdir=comparison/first
+seconddir=comparison/second
+
 # Make sure the output directory exists
 mkdir -p comparison