filesets: use example with quotes for encoding predicate
A user on IRC was confused that "encoding(ASCII)" works and
"encoding(UTF-8)" fails with "parse error: encoding requires an
encoding name".
import doctest, tempfile, os, sys
if __name__ == "__main__":
if 'TERM' in os.environ:
del os.environ['TERM']
fd, name = tempfile.mkstemp(suffix='hg-tst')
try:
os.write(fd, sys.stdin.read())
os.close(fd)
failures, _ = doctest.testfile(name, module_relative=False)
if failures:
sys.exit(1)
finally:
os.remove(name)