Improve bash quoting, and other similar best practices

This patch updates the shell scripts with some of the common best
practices, which should make them more resilient to unusual failures and
unexpected environments (in particular, directories with spaces).

Most of these were identified by shellcheck.

test/t-04-aliases/run.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 set -e
-. $(dirname ${0})/../util/lib.sh
+. "$(dirname "$0")/../util/lib.sh"
 
 init
 check_hostaliases
@@ -14,12 +14,12 @@ chasquid -v=2 --logfile=.logs/chasquid.log --config_dir=config &
 wait_until_ready 1025
 
 function send_and_check() {
-	run_msmtp $1@testserver < content
+	run_msmtp "$1@testserver" < content
 	shift
-	for i in $@; do
-		wait_for_file .mail/$i@testserver
-		mail_diff content .mail/$i@testserver
-		rm -f .mail/$i@testserver
+	for i in "$@"; do
+		wait_for_file ".mail/$i@testserver"
+		mail_diff content ".mail/$i@testserver"
+		rm -f ".mail/$i@testserver"
 	done
 }