Correct extconf usage.

ext/extconf.rb

@@ -15,11 +15,8 @@ else
   $CFLAGS << " -O3"
 end
 
-dir_config 'rlibmemcached'
-
-# XXX There's probably a better way to do this
-raise "shared library 'libmemcached' not found" unless 
-  find_library('memcached', 'memcached_server_add', *ENV['LD_LIBRARY_PATH'].to_s.split(":"))
+find_library(*['memcached', 'memcached_server_add', dir_config('libmemcached').last].compact) or
+  raise "shared library 'libmemcached' not found"
 
 [ 
   'libmemcached/memcached.h',
@@ -27,9 +24,9 @@ raise "shared library 'libmemcached' not found" unless
   'libmemcached/memcached_storage.h',
   'libmemcached/memcached_result.h',
   'libmemcached/memcached_server.h'
-].each do |header|
-  raise "header file '#{header}' not  found" unless 
-    find_header(header, *ENV['INCLUDE_PATH'].to_s.split(":"))
+].each do |header|  
+    find_header(*[header, dir_config('libmemcached').first].compact) or
+      raise "header file '#{header}' not  found"
 end
 
 create_makefile 'rlibmemcached'