Update requirements.txt

This commit updates requrements.txt by:
* updating versions of requirements
* ensuring packages installed only as dependencies of packages required
for python version below 2.7.9 have correct interpreter version requirement
for installation
* adding missing requirements, so that the file contains a complete list of
required packages and their dependencies, each with its version.

requirements.txt

@@ -1,22 +1,23 @@
-cachetools==1.1.5 ; python_version < '3'
-cffi==1.5.2 ; python_version < '3'
-cryptography==1.3 ; python_version < '3'
-decorator==4.0.9
-dnspython==1.12.0 ; python_version < '3'
+cachetools==1.1.6 ; python_version < '3'
+cffi==1.8.3 ; python_version < '2.7.9'
+cryptography==1.5 ; python_version < '2.7.9'
+decorator==4.0.10
 dnspython3==1.12.0 ; python_version >= '3'
-enum34==1.1.2 ; python_version < '3'
-funcsigs==0.4 ; python_version < '3'
+dnspython==1.14.0 ; python_version < '3'
+enum34==1.1.6 ; python_version < '2.7.9'
+funcsigs==1.0.2 ; python_version < '3'
 future==0.15.2
 idna==2.1
-ipaddress==1.0.16 ; python_version < '3'
-mock==1.3.0 ; python_version < '3'
-ndg-httpsclient==0.4.0 ; python_version < '2.7.9'
+ipaddress==1.0.17 ; python_version < '3'
+mock==2.0.0 ; python_version < '3'
+ndg-httpsclient==0.4.2 ; python_version < '2.7.9'
 nose-parameterized==0.5.0
-pbr==1.8.1 ; python_version < '3'
+pbr==1.10.0 ; python_version < '3'
 pyasn1==0.1.9 ; python_version < '2.7.9'
-pycparser==2.14 ; python_version < '3'
-pyOpenSSL==16.0.0 ; python_version < '2.7.9'
-requests==2.9.1
+pycparser==2.14 ; python_version < '2.7.9'
+pyOpenSSL==16.1.0 ; python_version < '2.7.9'
+requests-file==1.4
+requests==2.11.1
 six==1.10.0
-tldextract==1.7.5
-validators==0.10
+tldextract==2.0.1
+validators==0.11.0