The 'bin' folder is the version used when running the PhotoRec ingest module.  It is also the 32-bit version.
When the 64-bit version of the installer is created, the photorec_exec/64-bit/bin folder is placed at photorec_exec/bin. 
When the 32-bit version of the installer is created, the photorec_exec/64-bit folder is deleted.
See 'build-windows-installer.xml' for more details.