AAPT: Fix resource versioning

Resource generation was greedy, so when an attribute with sdk level 21 was used in a resource
with v1, and a different attribute with sdk level 21 was used in a resource with v11,
a v21 resource would be synthesized, but it would contain the attribute from v1 instead of v11.

This change fixes the issue, having the higher versioned resource take precedence.

Bug:22793816
Change-Id: Ia687f56b0d9969e424111477d55d9804255b22e9