Add bindings for X509_REQ_get_extensions.

Without this binding it is impossible to get any extension objects from an
X509Req object.
diff --git a/AUTHORS.rst b/AUTHORS.rst
index b9dc459..0e3979a 100644
--- a/AUTHORS.rst
+++ b/AUTHORS.rst
@@ -13,3 +13,4 @@
 * Alex Stapleton <alexs@prol.etari.at> (A1C7 E50B 66DE 39ED C847 9665 8E3C 20D1 9BD9 5C4C)
 * David Reid <dreid@dreid.org> (0F83 CC87 B32F 482B C726  B58A 9FBF D8F4 DA89 6D74)
 * Konstantinos Koukopoulos <koukopoulos@gmail.com> (D6BD 52B6 8C99 A91C E2C8  934D 3300 566B 3A46 726E)
+* Stephen Holsapple <sholsapp@gmail.com>