Ensure a UTF-8 locale is available for tests

Fixes Debian sid schroot build.

Also add build deps required for full testing:
tmux,  less (for window-resize.test)

debian/control

@@ -2,7 +2,7 @@ Source: mosh
 Section: net
 Priority: optional
 Maintainer: Keith Winstein <keithw@mit.edu>
-Build-Depends: debhelper (>= 9), autotools-dev, protobuf-compiler, libprotobuf-dev, dh-autoreconf, pkg-config, libutempter-dev, zlib1g-dev, libncurses5-dev, libssl-dev, bash-completion
+Build-Depends: debhelper (>= 9), autotools-dev, protobuf-compiler, libprotobuf-dev, dh-autoreconf, pkg-config, libutempter-dev, zlib1g-dev, libncurses5-dev, libssl-dev, bash-completion, locales, tmux, less
 Standards-Version: 3.9.8
 Homepage: https://mosh.org
 Vcs-Git: https://github.com/mobile-shell/mosh.git

src/tests/e2e-test

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+. "$(dirname "$0")/e2e-test-subrs"
+
 #
 # Validate that mosh produces expected output, using screen captures
 # in tmux.
@@ -106,6 +108,9 @@ mosh_server()
 }
 
 # main
+if ! set_locale; then
+    test_error "e2e-test: no usable locale\n"
+fi
 
 # Set up environment
 if [ -z "$srcdir" ]; then

src/tests/e2e-test-subrs

@@ -54,3 +54,24 @@ chr()
 {
     printf '%b' "\\0$(printf %03o "$1")"
 }
+
+# If the locale is not set to a UTF-8 locale, set it to en_US.UTF-8
+# or C.UTF-8.
+set_locale()
+{
+    # Test for a usable locale.
+    map=$(locale charmap 2>/dev/null)
+    if [ "$map" = "utf-8" ] || [ "$map" = "UTF-8" ]; then
+	return 0
+    fi
+    # Attempt to find/set a usable locale.
+    for i in en_US.UTF-8 en_US.utf8 C.UTF-8; do
+	map="$(env LANG=$i locale charmap 2>/dev/null)"
+	if [ "$map" = "utf-8" ] || [ "$map" = "UTF-8" ]; then
+	    export LANG=$i LC_ALL=''
+	    return 0
+	fi
+    done
+    # Fail.
+    return 1
+}

src/tests/local.test

@@ -1,4 +1,11 @@
 #!/bin/sh
+
+. "$(dirname "$0")/e2e-test-subrs"
+if ! set_locale; then
+    echo "$0: no usable locale" >&2
+    exit 99
+fi
+
 set -eu
 out=$(
     TERM=xterm \