For debugging: add env. variable MS_HTTP_HEADER that can be set to NO in the non-MOD_WMS_ENABLED mode to avoid emitting HTTP headers
Improve previous commit when msIO_setHeader() is called before any call to msIO_Initialize()
Remove MS_HTTP_HEADER hack to use mapserv -nh existing mechanism
Add -h/--help option to mapserv binary to display help message
Extend default message displayed when launching mapserv without argument, to advertize --help
Add comment to mention that MS_ENABLE_CGI_CL_DEBUG_ARGS is diabled because of security concerns
Add missing dll export