* ext/etc/etc.c: Etc.sysconf, Etc.confstr and IO#pathconf implemented.

* ext/etc/extconf.rb: Check sysconf(), confstr() and fpathconf().

* ext/etc/mkconstants.rb: New file.

 [ruby-core:62600] [Feature #9842]



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45984 b2dd03c8-39d4-4d8f-98ff-823fe69b080e