When running on Win64, you must run a 64-bit gvimext.dll to implement
the Edit with Vim functionality. Gvim.exe need not be 64-bit;
indeed, a 32-bit gvim.exe integrates better with the other language
interfaces, as many of them are not available in a 64-bit flavor.
Bram proposes that the NSIS installer, gvim.nsi, will use a 32-bit
version of install.exe to install a 64-bit gvimext.dll on Win64
and a 32-bit gvimext.dll on Win32. Either way, a 32-bit gvim.exe
would be installed.