Tests: skip tests not appropriate for win32.

Skip tests which doesn't work on win32, notably ones using crypt(),
symlinks and shared memory.
diff --git a/proxy_cache_lock.t b/proxy_cache_lock.t
index 6b47c60..f5c19e3 100644
--- a/proxy_cache_lock.t
+++ b/proxy_cache_lock.t
@@ -22,6 +22,8 @@
 select STDERR; $| = 1;
 select STDOUT; $| = 1;
 
+plan(skip_all => 'win32') if $^O eq 'MSWin32';
+
 my $t = Test::Nginx->new()->has(qw/http proxy cache/)
 	->write_file_expand('nginx.conf', <<'EOF');