fix issues #364 since postgres still calls it libpq on windows and the linker doesnt add the lib prefix automatically there

dub.json

@@ -474,7 +474,8 @@
 			"description": "Postgresql client library. Wraps the libpq C library with my database.d interface.",
 			"targetType": "library",
 			"dependencies": {"arsd-official:database_base":"*"},
-			"libs": ["pq"],
+			"libs-posix": ["pq"],
+			"libs-windows": ["libpq"],
 			"sourceFiles": ["postgres.d"],
 			"importPaths": ["."],
 			"dflags-dmd": ["-mv=arsd.postgres=$PACKAGE_DIR/postgres.d"],

postgres.d

@@ -23,7 +23,11 @@
 	should be found in the PostgreSQL lib and/or bin folders (check them both!).
 +/
 module arsd.postgres;
-pragma(lib, "pq");
+
+version(Windows)
+	pragma(lib, "libpq");
+else
+	pragma(lib, "pq");
 
 public import arsd.database;