[stdlib] Adding a deprecated version of flatMap to warn misuses.

[moiseev]

Due to implicit promotion to optional it is possible to call flatMap
with a closure, that does not return an optional. This way the code
works, but is unnecessary inefficient. Such uses of flatMap can and
should be replaced with map.

[moiseev]

@swift-ci Please test

[swift-ci]

Build failed
Jenkins build - Swift Test OS X Platform
Git Commit - 0198a4e58fbeaedf42727d81cc21ebfc00182ae5
Test requested by - @moiseev

[swift-ci]

Build failed
Jenkins build - Swift Test Linux Platform
Git Commit - 0198a4e58fbeaedf42727d81cc21ebfc00182ae5
Test requested by - @moiseev

[airspeedswift]

Should this really be an error or just a warning?

edit: sorry I see it is just a warning. The test is failing with an error tho.

[moiseev]

@airspeedswift Yeah, -verify mode treats unexpected warnings as errors. Fixing the tests is on my list.

[moiseev]

@swift-ci Please test

[swift-ci]

Build failed
Jenkins build - Swift Test Linux Platform
Git Commit - 0198a4e58fbeaedf42727d81cc21ebfc00182ae5
Test requested by - @moiseev

[swift-ci]

Build failed
Jenkins build - Swift Test OS X Platform
Git Commit - 0198a4e58fbeaedf42727d81cc21ebfc00182ae5
Test requested by - @moiseev