Fixed exports to use OPENEXR_DLL when doing DLL and DSO builds.
Fixed exports for several Imf classes.
Changing the include syntax from <> to ""
Merge remote-tracking branch 'upstream/export-fixes' into v2-ev-cmake

Preserves most of the remote branch changes, but added some customizations to keep it building properly under msvc.
Merge branch 'develop' into v2-ev-cmake