merge revision(s) r45225,r45240,r45488: [Backport #9578] [Backport #9630]

	* ext/readline/readline.c (Init_readline): Use rl_hook_func_t instead
	  of Function to support readline-6.3.  (rl_hook_func_t is available
	  since readline-4.2.)
	  Reported by Dmitry Medvinsky.  [ruby-core:61141] [Bug #9578]

	* ext/readline/extconf.rb (rl_hook_func_t): define as Function for
	  very old readline versions.  [ruby-core:61209] [Bug #9578]

	* ext/readline/extconf.rb: fix typo, `$defs` not `$DEFS`.
	  [ruby-core:61756] [Bug #9578]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@45772 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merge revision(s) r45518: [Backport #9578] [Backport #9630] [Backport #9702]

	* ext/readline/extconf.rb (rl_hook_func_t): check pointer type.
	  [ruby-dev:48089] [Bug #9702]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@45773 b2dd03c8-39d4-4d8f-98ff-823fe69b080e