Fix linking bundled zlib

* Prefix "./" to the import library name to expanded when static
  linking exts.

* Copy zlib shared library to the top build directory.

ext/zlib/extconf.rb

@@ -46,7 +46,7 @@ else
       end
       m = File.read(m)
       zimplib = m[/^IMPLIB[ \t]*=[ \t]*(\S+)/, 1]
-      $LOCAL_LIBS << " " << zimplib
+      ($LOCAL_LIBS << " ./" << zimplib).strip!
       unless $nmake or /^TOP[ \t]/ =~ m
         m.gsub!(/win32\/zlib\.def/, '$(TOP)/\&')
         m.gsub!(/^(\t.*[ \t])(\S+\.rc)/, '\1-I$(<D) $<')
@@ -62,7 +62,7 @@ else
         "$(TARGET_SO): $(ZIMPLIB)\n",
         "$(ZIMPLIB):\n",
         "#{zmk} $(ZOPTS) $@\n",
-        "install-so: $(topdir)/#{dll}",
+        "install-so static: $(topdir)/#{dll}",
         "$(topdir)/#{dll}: $(ZIMPLIB)\n",
         "\t$(Q) $(COPY) #{dll} $(@D)\n",
         "clean: clean-zsrc\n",