Stop segfaulting at the end of mach bootstrap

`mach bootstrap` will finish succesfully,
but then segfault inside glibc while exiting.
It seems to have to do with the MarkupSafe library used by Mako;
delaying the Mako import from the top level to inside functions where it
is used avoids the problem.
(It seems to interact with the call to pip to install the Salt
requirements in the virtualenv, as commenting that pip call out
separately will also fix the segfault.)

Also, use the Mako installed in the Python virtualenv while running
packaging commands (instead of the one from the bundled zip file),
and cleanup imports in the package_commands.py file.

python/servo/package_commands.py

@@ -9,36 +9,30 @@
 
 from __future__ import print_function, unicode_literals
 
-import sys
-import os.path as path
-sys.path.append(path.join(path.dirname(sys.argv[0]), "components", "style", "properties", "Mako-0.9.1.zip"))
-
 import json
 import os
+import os.path as path
 import shutil
 import subprocess
-import mako.template
-
-from mach.registrar import Registrar
 
 from mach.decorators import (
     CommandArgument,
     CommandProvider,
     Command,
 )
-
-from mako.template import Template
+from mach.registrar import Registrar
+# Note: mako cannot be imported at the top level because it breaks mach bootstrap
 
 from servo.command_base import (
     archive_deterministically,
     BuildNotFound,
     cd,
     CommandBase,
+    find_dep_path_newest,
     is_macosx,
     is_windows,
     get_browserhtml_path,
 )
-from servo.command_base import find_dep_path_newest
 
 
 def delete(path):
@@ -221,6 +215,7 @@ def package(self, release=False, dev=False, android=None, debug=False, debugger=
                 raise Exception("Error occurred when getting Servo version: " + stderr)
             version = "Nightly version: " + version
 
+            import mako.template
             template_path = path.join(dir_to_resources, 'Credits.rtf.mako')
             credits_path = path.join(dir_to_resources, 'Credits.rtf')
             with open(template_path) as template_file:
@@ -299,8 +294,9 @@ def package(self, release=False, dev=False, android=None, debug=False, debugger=
             change_prefs(dir_to_resources, "windows")
 
             # generate Servo.wxs
+            import mako.template
             template_path = path.join(dir_to_root, "support", "windows", "Servo.wxs.mako")
-            template = Template(open(template_path).read())
+            template = mako.template.Template(open(template_path).read())
             wxs_path = path.join(dir_to_msi, "Servo.wxs")
             open(wxs_path, "w").write(template.render(
                 exe_path=target_dir,