[[ VS2015 ]] Tweak libpq so it builds under VS2015

This patch ensures that libpq builds under VS2015. It tweaks a
win32 compatibility routine definition based on VS version and
ensure win32error.c is included in the build which provides the
_dosmaperr function which is no longer present in the VS CRT.

Author: runrevmark

libpq/libpq.gyp

@@ -111,6 +111,7 @@
 										'src/system.c',
 										'src/win32.c',
 										'src/win32setlocale.c',
+										'src/win32error.c',
 									],
 
 									'link_settings':

libpq/src/chklocale.c

@@ -203,7 +203,7 @@ win32_langinfo(const char *ctype)
 {
 	char	   *r = NULL;
 
-#if (_MSC_VER >= 1700)
+#if (_MSC_VER == 1700)
 	_locale_t	loct = NULL;
 
 	loct = _create_locale(LC_CTYPE, ctype);