wscript: set default prefix, do not install without destdir as we don't follow typical unix filesystem hierarchy

wscript

@@ -10,6 +10,7 @@ import re
 VERSION = '2.4'
 APPNAME = 'hlsdk-portable'
 top = '.'
+default_prefix = '/'
 
 Context.Context.line_just = 60 # should fit for everything on 80x26
 
@@ -238,6 +239,9 @@ def configure(conf):
 	conf.add_subproject('cl_dll')
 
 def build(bld):
+	if bld.is_install and not bld.options.destdir:
+		bld.fatal('Set the install destination directory using --destdir option')
+
 	# don't clean QtCreator files and reconfigure saved options
 	bld.clean_files = bld.bldnode.ant_glob('**',
 		excl='*.user configuration.py .lock* *conf_check_*/** config.log %s/*' % Build.CACHE_DIR,