Merge pull request #540 from khawkins/unstable

Mobile SDK: Merging master into unstable
App could crash if snapshot view was already presented
Merge pull request #542 from khawkins/fix_snapshot_crash

App could crash if snapshot view was already presented
Project file changes to support archiving
Merge pull request #546 from khawkins/archive_header_paths

Project file changes to support archiving
Merge remote-tracking branch 'origin/master' into unstable

Conflicts:
	native/SampleApps/NativeSqlAggregator/NativeSqlAggregator.xcodeproj/project.pbxproj
	shared/SalesforceNetworkSDK