pgsql: Copy the libpq DLL to the bin directory on Mingw and Cygwin.

Copy the libpq DLL to the bin directory on Mingw and Cygwin.

This has long been done by the MSVC build system, and has caused
confusion in the past when programs like psql have failed to start
because they can't find the DLL. If it's in the same directory as it now
will be they will find it.

Backpatch to all live branches.

Branch
------
REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/1e9876c3b69491906cfcd542ebc8c79e91df6904

Modified Files
--------------
src/interfaces/libpq/Makefile |    9 +++++++++
1 file changed, 9 insertions(+)