Added logging and proper execution of commands

Fixed several issues, and ran a basic test on ironsmith itself.

Need to prevent subsequent builds on same versions

exec.go

@@ -0,0 +1,33 @@
+// Copyright 2016 Tim Shannon. All rights reserved.
+// Use of this source code is governed by the MIT license
+// that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+func runCmd(cmd, dir string) ([]byte, error) {
+	s := strings.Fields(cmd)
+
+	var args []string
+
+	if len(s) > 1 {
+		args = s[1:]
+	}
+
+	ec := exec.Command(s[0], args...)
+
+	ec.Dir = dir
+
+	vlog("Executing command: %s in dir %s\n", cmd, dir)
+
+	result, err := ec.CombinedOutput()
+	if err != nil {
+		return nil, fmt.Errorf("%s:\n%s", err, result)
+	}
+	return result, nil
+}