proxy-call: Use g_error_set_literal for content from the web server
proxy-call: Use g_error_set_literal for content from the web server

Fixes: http://bugs.meego.com/show_bug.cgi?id=6295

ThomasBollmeier/librest-oauth-proxy,Distrotech/librest,GNOME/librest,GNOME/librest,GNOME/librest,ThomasBollmeier/librest-oauth-proxy,Distrotech/librest