Don't assume SO_UPDATE_CONNECT_CONTEXT is defined.

Fixes boost trac ticket #10016.
Use VerifyVersionInfo rather than GetVersionEx.

GetVersionEx has been deprecated.
Fix off-by-one error in signal number check.

Fixes boost trac ticket #9324.
Return bytes transferred when ReadFile fails with ERROR_MORE_DATA.

Reverted the previous change to ignore ERROR_MORE_DATA. Instead,
the error will propagated as with any other (i.e. in an error_code
or thrown as a system_error). For code that needs to handle partial
messages, the error_code overload should be used.

Fixes boost trac ticket #10034.
Work around gcc problem to do with anonymous enums.

Fixes boost trac ticket #10042.
Use SSE2 intrinsics to allow the Cray compiler to work.