add getpgrp support in os mod

vm/src/stdlib/os.rs

@@ -1194,6 +1194,11 @@ fn os_getpgid(pid: u32, vm: &VirtualMachine) -> PyResult {
     }
 }
 
+#[cfg(unix)]
+fn os_getpgrp(vm: &VirtualMachine) -> PyResult {
+    Ok(vm.new_int(unistd::getpgrp().as_raw()))
+}
+
 #[cfg(all(unix, not(target_os = "redox")))]
 fn os_getsid(pid: u32, vm: &VirtualMachine) -> PyResult {
     match unistd::getsid(Some(Pid::from_raw(pid as i32))) {
@@ -1620,6 +1625,7 @@ fn extend_module_platform_specific(vm: &VirtualMachine, module: &PyObjectRef) {
         "getegid" => ctx.new_function(os_getegid),
         "getpgid" => ctx.new_function(os_getpgid),
         "getuid" => ctx.new_function(os_getuid),
+        "getpgrp" => ctx.new_function(os_getpgrp),
         "geteuid" => ctx.new_function(os_geteuid),
         "pipe" => ctx.new_function(os_pipe), //TODO: windows
         "set_blocking" => ctx.new_function(os_set_blocking),