Since commit cb4a3b04 we were already doing this for the Cygwin/mingw
toolchains, but MSVC had not been updated to do it.  At Install.pm time,
the Makefile (or GNUmakefile) is inspected, and if a line matching
SO_MAJOR_VERSION is found (indicating a shared library is being built),
then files with the .dll extension are set to be installed in bin/
rather than lib/, while files with .lib extension are installed in lib/.
This makes the MSVC toolchain up to date with cygwin/mingw.

This removes ad-hoc hacks that were copying files into bin/ or lib/
manually (libpq.dll in particular was already being copied into bin).
So while this is a rather ugly kludge, it's still cleaner than what was
there before.

Author: Michael Paquier
Reviewed by: Asif Naeem