tools: Apply `set -x` to just the interesting parts of *-pull-request.

The Git commands we're invoking to do the real work are useful to
print, for transparency to see what's happening and that there's no
magic here.

The boring shell stuff like `remote=${2:-"upstream"}` is not so
helpful, and nor is the rather arcane and in any case read-only
command `git diff-index --quiet HEAD`.  Those only add noise that
obscures the interesting parts.  So, move the `set -x` down to when
we're done with the boring preparatory stuff and ready to perform
the commands that do the work.

tools/fetch-pull-request

@@ -1,16 +1,17 @@
 #!/usr/bin/env bash
 set -e
-set -x
 
 if ! git diff-index --quiet HEAD; then
-    set +x
     echo "There are uncommitted changes:"
     git status --short
     echo "Doing nothing to avoid losing your work."
     exit 1
 fi
+
 request_id="$1"
 remote=${2:-"upstream"}
+
+set -x
 git fetch "$remote" "pull/$request_id/head"
 git checkout -B "review-original-${request_id}"
 git reset --hard FETCH_HEAD

tools/fetch-rebase-pull-request

@@ -1,16 +1,17 @@
 #!/usr/bin/env bash
 set -e
-set -x
 
 if ! git diff-index --quiet HEAD; then
-    set +x
     echo "There are uncommitted changes:"
     git status --short
     echo "Doing nothing to avoid losing your work."
     exit 1
 fi
+
 request_id="$1"
 remote=${2:-"upstream"}
+
+set -x
 git fetch "$remote" "pull/$request_id/head"
 git checkout -B "review-${request_id}" "$remote/master"
 git reset --hard FETCH_HEAD