Clear SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS without SSL_CTX_clear_options()

Clear SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS without SSL_CTX_clear_options()

A patch to clear SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS was added recently:

  http://gitorious.org/fetchmail/fetchmail/commit/48809c5b9f6c9081f4031fa938dd63b060c18a4b?format=patch

Older implementations of OpenSSL do not support SSL_CTX_clear_options().

This patch reworks the previous change to avoid the use of
SL_CTX_clear_options() and instead clears the corresponding bit in
SSL_OP_ALL before calling SSL_CTX_set_options().