• internal: Optimize HTTP transport parameters
• aetest: Fix Federated-Identity headers in the new environment

aetest: fixes to app.yaml
go.mod updates

delay: fix func stable name to strip gopath prefix

Increase internal.limitDial's timeout from 500ms to 10s, to account for differences in the go111 legacy API endpoint.

• Simplified the capabilities API to remove unnecessary RPC calls
• Fixes to stderr handling in the aetest package

Fix a couple typos and update the versions of dependencies in go.mod.

• Add datastore.EnableKeyConversion for compatibility with Cloud Datastore

• Fix RunInBackground when using dev_appserver
• Add DistinctOn support to datastore

• Don't mirror log messages to stderr on App Engine Second Generation (Go 1.11 and above) to cut down on log noise.
• Add SupportDatastoreEmulator field to aetest Options.
• Add support for stable delay.Func keys in App Engine Second Generation.

• Removes support for Go < 1.9
• Ensure at least one log flush happens before connections are closed when using Go 1.11 on App Engine Standard
• Add appengine.IsStandard(), appengine.IsFlex(), and appengine.IsAppengine(), which report which Google infrastructure you are using