Handle gpg signing better (#1123)

Instead of checking whether it was set previously, setting it to false,
then setting it back to true if it was true before, just use the
command-line argument in git to override the config for that command.
Using a variable makes it pretty painless to do.

paper

@@ -23,6 +23,7 @@ while [ -h "$SOURCE" ]; do # resolve $SOURCE until the file is no longer a symli
 done
 SOURCE=$([[ "$SOURCE" = /* ]] && echo "$SOURCE" || echo "$PWD/${SOURCE#./}")
 basedir=$(dirname "$SOURCE")
+gitcmd="git -c commit.gpgsign=false"
 
 source "$basedir/scripts/functions.sh"
 
@@ -104,7 +105,7 @@ case "$1" in
                 set -e
 
                 paperstash
-                git rebase -i upstream/upstream
+                $gitcmd rebase -i upstream/upstream
                 paperunstash
             )
             ;;
@@ -115,7 +116,7 @@ case "$1" in
                 set -e
 
                 paperstash
-                git rebase -i upstream/upstream
+                $gitcmd rebase -i upstream/upstream
                 paperunstash
             )
             ;;
@@ -125,9 +126,9 @@ case "$1" in
             (
                 set -e
 
-                git add .
-                git commit --amend
-                git rebase --continue
+                $gitcmd add .
+                $gitcmd commit --amend
+                $gitcmd rebase --continue
 
                 cd "$basedir"
                 scripts/rebuildPatches.sh "$basedir"