This fixes various issues related to gcc's strict-aliasing warning
by using unions. It also handles various cases hit with
gcc's missing-declarations warning.
Using platform-neutral osinclude.h makes it easier to substitute
implementation when necessary and eliminates some variability between
build configurations.
* Linux folder has been renamed to Unix, to match defines and so that it
compiles on OS X.
* This removes the need for a per-platform include search path for the
right OS folder
