Check SDK major version as well as revision
Check SDK major version as well as revision

Recent versions of the SDK (39 and above) don't
share a global revision space with the other SDKs.
Each branch starts at revision 1.

This change is needed to fix the NaCl SDK builder
for pepper_40 which is currently failing because
its detecting the wrong pnacl install location.

BUG=432273
R=binji@chromium.org

Review URL: https://codereview.chromium.org/715873003

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