* ext/zlib/extconf.rb: detect z_crc_t type which will be defined
	  since zlib-1.2.7.

	* ext/zlib/zlib.c (rb_zlib_crc_table): use z_crc_t if available.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@36939 b2dd03c8-39d4-4d8f-98ff-823fe69b080e