dynamic loading on NT works!

Hi all,

I have played with dynamic loading of modules to the backend and it works.
It needs only to add "DLLIMPORT" to all data structures, that should be
exported.

The main thing is done in the src/include/c.h - it defines DLLIMPORT to
nothing on platforms other then Cygwin and __declspec(...) on Cygwin, and in
src/makefiles/Makefile.win - it defines the symbol BUILDING_DLL only when
the make process is in the src/backend subtree.

I have tested it with trigger regression test - it works, and with some
plpgsql stuff - it doesn't work and it probably needs some other data to be
exported from the backend.

I think the changes are minimal so they can by applied to the development
source tree for 6.5.

            Dan

----------------------------------------------
Daniel Horak
network and system administrator
e-mail: horak@mmp.plzen-city.cz
privat e-mail: dan.horak@email.cz
----------------------------------------------