sync with master branch to backport some fixes
    
    - Use 1024bit DH key in test_ssl (Matej Stuchlik)
    - Use -O0 when compiling -debug build (Matej Stuchlik)
    - Update pip version variable to the version we actually ship (Matej Stuchlik)
    - Fixed undefined behaviour in faulthandler which caused test to hang on x86_64
      (http://bugs.python.org/issue23433) (Matej Stuchlik)