Explicitly depend upon the http_postpone_filter_module

Previously mod_zip would mangle the output chain if another module
did not happen to require the postpone_filter module. By making this
dependency explicit we can avoid a bug when nginx is compiled with
certain configuration options.

Fixes evanmiller#17

.travis.yml

@@ -34,5 +34,5 @@ script:
 
 env:
   - NGINX_VERSION="1.6.2"
-  - NGINX_VERSION="1.7.10"
+  - NGINX_VERSION="1.7.12"
 

config

@@ -5,6 +5,10 @@ NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_zip_parsers.c"
 NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_zip_file.c"
 NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_zip_headers.c"
 
+
+# This module depends upon the postpone filter being activated
+HTTP_MODULES="$HTTP_MODULES ngx_http_postpone_filter"
+
 ngx_feature="iconv_open()"
 ngx_feature_name="NGX_ZIP_HAVE_ICONV"
 ngx_feature_run=no