Issue-128: allow use Barnett's regexs in pexpect

Pexpect checks explicitly for Python's regexs rejecting Barnett's one.
The adapter closes the gap between this two and allow to use Barnett's
regex with pexpect.

byexample/runner.py

@@ -1,6 +1,6 @@
 from __future__ import unicode_literals
 import pexpect, time, termios, operator, os, itertools, contextlib
-import re as re_orig
+import re as python_re
 from . import regex as re
 from functools import reduce, partial
 from .executor import TimeoutException, InputPrefixNotFound
@@ -80,6 +80,43 @@ def cancel(self, example, options):
         return False
 
 
+class PexpectSpawnAdapter(pexpect.spawn):
+    def compile_pattern_list(self, patterns):
+        ''' This is an extension of pexpect.spawn.compile_pattern_list
+            to accept not only Python's regex objects (re module) but
+            also Barnett's regexs (third-party regex module).
+
+            This is a workaround for the issue #655
+            (https://github.com/pexpect/pexpect/issues/655)
+            '''
+        if patterns is None:
+            return []
+        if not isinstance(patterns, list):
+            patterns = [patterns]
+
+        # Allow dot to match \n
+        compile_flags = python_re.DOTALL
+        if self.ignorecase:
+            compile_flags = compile_flags | python_re.IGNORECASE
+        compiled_pattern_list = []
+        cls = pexpect.spawnbase
+        for idx, p in enumerate(patterns):
+            if isinstance(p, self.allowed_string_types):
+                p = self._coerce_expect_string(p)
+                compiled_pattern_list.append(python_re.compile(p, compile_flags))
+            elif p is cls.EOF:
+                compiled_pattern_list.append(cls.EOF)
+            elif p is cls.TIMEOUT:
+                compiled_pattern_list.append(cls.TIMEOUT)
+            elif isinstance(p, type(python_re.compile(''))):
+                compiled_pattern_list.append(p)
+            elif isinstance(p, type(re.compile(''))):  # <-- the workaround
+                compiled_pattern_list.append(p)
+            else:
+                self._pattern_type_err(p)
+        return compiled_pattern_list
+
+
 class PexpectMixin(object):
     def __init__(self, PS1_re, any_PS_re):
         self.PS1_re = re.compile(PS1_re)
@@ -106,7 +143,7 @@ def _spawn_interpreter(
         env.update({'LINES': str(rows), 'COLUMNS': str(cols)})
 
         self._drop_output()  # there shouldn't be any output yet but...
-        self.interpreter = pexpect.spawn(
+        self.interpreter = PexpectSpawnAdapter(
             cmd,
             echo=False,
             encoding=self.encoding,