Assuming that the terminal running mosh in Termux supports 256
colors should be safe, and avoids a popen() call which uses
/system/bin/sh and may not always work.
Set the -l flags ("Locale-related environment variable to try as
part of a fallback environment, if the startup environment does
not specify a character set of UTF-8") when invoking mosh-server
just like the perl script does. Fixes#288.
