py-pendulum: Disable C Extensions when building the 2.7 multi-package

C Extensions code does not seem supported when it is built with Python 2.7.
Pass the environment variable to avoid compiling it and failing and adjust PLIST
accordingly.

Index: Makefile
===================================================================
RCS file: /cvsroot/pkgsrc/time/py-pendulum/Makefile,v
retrieving revision 1.10
diff -u -p -r1.10 Makefile
--- Makefile	7 Aug 2018 10:09:43 -0000	1.10
+++ Makefile	14 Aug 2018 13:58:41 -0000
@@ -18,5 +18,12 @@ DEPENDS+=	${PYPKGPREFIX}-tzdata>=2018.3:
 DEPENDS+=	${PYPKGPREFIX}-typing-[0-9]*:../../devel/py-typing
 .endif
 
+#
+# XXX: C Extensions code is only supported with Python 3
+#
+.if "${PYPKGPREFIX}" == "py27"
+MAKE_ENV+=	PENDULUM_EXTENSIONS=0
+.endif
+
 .include "../../lang/python/distutils.mk"
 .include "../../mk/bsd.pkg.mk"
Index: PLIST
===================================================================
RCS file: /cvsroot/pkgsrc/time/py-pendulum/PLIST,v
retrieving revision 1.5
diff -u -p -r1.5 PLIST
--- PLIST	16 Jun 2018 13:06:54 -0000	1.5
+++ PLIST	14 Aug 2018 13:58:41 -0000
@@ -10,7 +10,7 @@ ${PYSITELIB}/pendulum/_extensions/__init
 ${PYSITELIB}/pendulum/_extensions/__init__.pyc
 ${PYSITELIB}/pendulum/_extensions/__init__.pyo
 ${PYSITELIB}/pendulum/_extensions/_helpers.c
-${PYSITELIB}/pendulum/_extensions/_helpers.so
+${PLIST.py3x}${PYSITELIB}/pendulum/_extensions/_helpers.so
 ${PYSITELIB}/pendulum/_extensions/helpers.py
 ${PYSITELIB}/pendulum/_extensions/helpers.pyc
 ${PYSITELIB}/pendulum/_extensions/helpers.pyo
@@ -159,7 +159,7 @@ ${PYSITELIB}/pendulum/parsing/__init__.p
 ${PYSITELIB}/pendulum/parsing/__init__.pyc
 ${PYSITELIB}/pendulum/parsing/__init__.pyo
 ${PYSITELIB}/pendulum/parsing/_iso8601.c
-${PYSITELIB}/pendulum/parsing/_iso8601.so
+${PLIST.py3x}${PYSITELIB}/pendulum/parsing/_iso8601.so
 ${PYSITELIB}/pendulum/parsing/exceptions/__init__.py
 ${PYSITELIB}/pendulum/parsing/exceptions/__init__.pyc
 ${PYSITELIB}/pendulum/parsing/exceptions/__init__.pyo