Delay hash lookups until we are about to hit an exception.  This
gives a minor speedup ratio of 2-3% in the new bm_io_nonblock_noex
benchmark as well as reducing code.

* benchmark/bm_io_nonblock_noex.rb: new benchmark
* ext/openssl/ossl_ssl.c (no_exception_p): new function
  (ossl_start_ssl): adjust for no_exception_p
  (ossl_ssl_connect): adjust ossl_start_ssl call
  (ossl_ssl_connect_nonblock): ditto
  (ossl_ssl_accept): ditto
  (ossl_ssl_accept_nonblock): ditto
  (ossl_ssl_read_internal): adjust for no_exception_p
  (ossl_ssl_write_internal): ditto
  (ossl_ssl_write): adjust ossl_write_internal call
  (ossl_ssl_write_nonblock): ditto
* ext/stringio/stringio.c (strio_read_nonblock):
  delay exception check
* io.c (no_exception_p): new function
  (io_getpartial): call no_exception_p
  (io_readpartial): adjust for io_getpartial
  (get_kwargs_exception): remove
  (io_read_nonblock): adjust for io_getpartial,
  check no_exception_p on EOF
  (io_write_nonblock): call no_exception_p
  (rb_io_write_nonblock): do not check `exception: false'
  (argf_getpartial): adjust for io_getpartial
  [ruby-core:69778] [Feature #11318]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51113 b2dd03c8-39d4-4d8f-98ff-823fe69b080e