contrib/buildsystems: fix Visual Studio Debug configuration

contrib/buildsystems: fix Visual Studio Debug configuration

Even though Debug configuration builds, the resulting build is incorrect
in a subtle way: it mixes up Debug and Release binaries, which in turn
causes hard-to-predict bugs.

In my case, when git calls iconv library, iconv sets 'errno' and git
then tests it, but in Debug and Release CRT those 'errno' are different
memory locations.

This patch addresses 3 connected bugs:
1) Typo in '\(Configuration)'. As a result, Debug configuration
   condition is always false and Release path is taken instead.
2) Regexp that replaced 'zlib.lib' with 'zlibd.lib' was only affecting
   the first occurrence. However, some projects have it listed twice.
   Previously this bug was hidden, because Debug path was never taken.
   I decided that avoiding double -lz in makefile is fragile and I'd
   better replace all occurrences instead.
3) In Debug, 'libcurl-d.lib' should be used instead of 'libcurl.lib'.
   Previously this bug was hidden, because Debug path was never taken.

Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Acked-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>