Replace arguments for toggling socketengines  with --socketengine.
Merge pull request #585 from SaberUK/master+configure-engine-selection

Replace arguments for toggling socketengines  with --socketengine.
Use the preprocessor to check for TCP deferring support.
Merge pull request #587 from SaberUK/master+defer-preprocessor

Use the preprocessor to check for TCP deferring support.
Fix some warnings which are causing debug builds to fail.

- Clang: private field 'module' is not used
- GCC: suggest a space before ‘;’ or explicit braces around empty
       body in ‘while’ statement
Merge pull request #589 from SaberUK/master+fix-debug-build

Fix some warnings which are causing debug builds to fail.