tools: Use require_clean_work_tree everywhere.

As described in the commit that added this function, this fixes one
quite annoying bug and one at least in-principle bug:

 * On Windows, the simple version (lacking `git update-index
   --refresh`) routinely gives false positives, making the tools
   that rely on it basically unusable.

 * If you have uncommitted changes in the index but manage to have
   the worktree nevevertheless match HEAD, the simple version will
   give a false negative and we'd blow away those changes.

tools/fetch-pull-request

@@ -1,12 +1,11 @@
 #!/usr/bin/env bash
 set -e
 
-if ! git diff-index --quiet HEAD; then
-    echo "There are uncommitted changes:"
-    git status --short
-    echo "Doing nothing to avoid losing your work."
-    exit 1
-fi
+this_file=$(readlink -f "${BASH_SOURCE[0]}")
+# shellcheck source=lib/git-tools.bash
+. "${this_file%/*}"/lib/git-tools.bash
+
+require_clean_work_tree 'check out PR as branch'
 
 request_id="$1"
 remote=${2:-"upstream"}

tools/fetch-rebase-pull-request

@@ -1,12 +1,11 @@
 #!/usr/bin/env bash
 set -e
 
-if ! git diff-index --quiet HEAD; then
-    echo "There are uncommitted changes:"
-    git status --short
-    echo "Doing nothing to avoid losing your work."
-    exit 1
-fi
+this_file=$(readlink -f "${BASH_SOURCE[0]}")
+# shellcheck source=lib/git-tools.bash
+. "${this_file%/*}"/lib/git-tools.bash
+
+require_clean_work_tree 'check out PR as branch'
 
 request_id="$1"
 remote=${2:-"upstream"}

tools/reset-to-pull-request

@@ -39,13 +39,11 @@ if [ -z "$request_id" ]; then
     usage
 fi
 
-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
+this_file=$(readlink -f "${BASH_SOURCE[0]}")
+# shellcheck source=lib/git-tools.bash
+. "${this_file%/*}"/lib/git-tools.bash
+
+require_clean_work_tree 'reset to PR'
 
 if [ -z "$pseudo_remote" ]; then
     set -x