Dynamic modules.

The auto/module script is extended to understand ngx_module_link=DYNAMIC.
When set, it links the module as a shared object rather than statically
into nginx binary.  The module can later be loaded using the "load_module"
directive.

New auto/module parameter ngx_module_order allows to define module loading
order in complex cases.  By default the order is set based on ngx_module_type.

3rd party modules can be compiled dynamically using the --add-dynamic-module
configure option, which will preset ngx_module_link to "DYNAMIC" before
calling the module config script.

Win32 support is rudimentary, and only works when using MinGW gcc (which
is able to handle exports/imports automatically).

In collaboration with Ruslan Ermilov.
diff --git a/auto/cc/msvc b/auto/cc/msvc
index 393ba32..e588c48 100644
--- a/auto/cc/msvc
+++ b/auto/cc/msvc
@@ -118,6 +118,12 @@
 CORE_LINK="$NGX_RES $CORE_LINK"
 
 
+# dynamic modules
+#MAIN_LINK="-link -def:$NGX_OBJS/nginx.def"
+#MODULE_LINK="-LD $NGX_OBJS/nginx.lib"
+
+
+ngx_pic_opt=
 ngx_objout="-Fo"
 ngx_binout="-Fe"
 ngx_objext="obj"