.gitignore: touch up the entries regarding Visual Studio

Add the Microsoft .manifest pattern, and do not anchor the 'Debug'
and 'Release' entries at the top-level directory, to allow for
multiple projects (one per target).

Signed-off-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -230,6 +230,7 @@
 *.ipdb
 *.dll
 .vs/
-/Debug/
-/Release/
+*.manifest
+Debug/
+Release/
 *.dSYM