Makefile.sub: skip timezone tests

* win32/Makefile.sub (TZ): empty to skip timezone tests which are not
  supported on Windows.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43289 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_array.rb: add test

* test/ruby/test_array.rb (test_last2): add test for Array#last with
  length argument.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43290 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
array.c: reduce RARRAY_LEN and ARY_CAPA

* array.c: reduce use of RARRAY_LEN and ARY_CAPA when object is not
  modified.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43291 b2dd03c8-39d4-4d8f-98ff-823fe69b080e