Set DX stack size to 1M by default on Windows.

Set DX stack size to 1M by default on Windows.

Bug: http://code.google.com/p/android/issues/detail?id=15181

Summary of bug: some user reported issues running dx.bat and
Fadden figured out the VM's stack size default was too small.
Using -Xss1m fixed it.

This CL introduces a default of -Xss1m and the usual mechanism
to override it using -JXssNm (like for -JXmx...)

Change-Id: I9769316c1708f08c91b93e07bd6d713a10561ea2