patch 7.4.794
Problem:    Visual Studio 2015 is not recognized.
Solution:   Add the version numbers to the makefile. (Taro Muraoka)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index 722127d..7cb7245 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -446,7 +446,7 @@
 !if "$(_NMAKE_VER)" == "12.00.21005.1"
 MSVCVER = 12.0
 !endif
-!if ("$(_NMAKE_VER)" == "14.00.22609.0") || ("$(_NMAKE_VER)" == "14.00.22816.0")
+!if ("$(_NMAKE_VER)" == "14.00.22609.0") || ("$(_NMAKE_VER)" == "14.00.22816.0") || ("$(_NMAKE_VER)" == "14.00.23026.0")
 MSVCVER = 14.0
 !endif
 !endif