functions when OPENSSL_NO_SSL2 is defined.
Usually openssl's header and the library (libssl) have the same
set of functions, but on some environment the library has functions
whose headers doesn't declare. (openssl/opensslconf.h and libsso.so
aren't be synchronized)
To detect such case explicitly check feature macro and remove
related functions.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54950 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
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