Make semantic_version.py usable outside of GAE

Make semantic_version.py usable outside of GAE

Take this if you like, not a big deal. Otherwise I will keep a patch file that I apply on updates.

BUG=
R=nweiz@google.com

Committed: https://github.com/dart-lang/pub-dartlang/commit/4987ef969042e1e3d9e619e1684c54d6fdda038a

[ricow1, 2014-09-09 07:17:57]

ricow@google.com changed reviewers:
+ rnystrom@google.com

[Bob Nystrom, 2014-09-09 16:22:18]

rnystrom@google.com changed reviewers:
+ nweiz@google.com

[Bob Nystrom, 2014-09-09 16:22:19]

I'd be fine with just always throwing ValueError here and removing the AppEngine
dependency entirely, but I'm not that familiar with this code. Deferring to
Natalie.

[nweiz, 2014-09-09 19:12:47]

On 2014/09/09 16:22:19, Bob Nystrom wrote:
> I'd be fine with just always throwing ValueError here and removing the
AppEngine
> dependency entirely, but I'm not that familiar with this code. Deferring to
> Natalie.

I'm fine with making this a plain ValueError. I think in practice
pub.dartlang.org never hits this.

[ricow1, 2014-09-10 06:02:09]

Changed to ValueError

[nweiz, 2014-09-10 18:32:41]

lgtm

[ricow1, 2014-09-11 12:12:56]

Committed patchset #2 (id:20001) manually as 4987ef9 (presubmit successful).