Set the default help format to html for msys builds.

This resolves issue msysgit#19 by setting the compiled default to html in msys
builds following the changes introduced by commit
1cc8af0 "help: use HTML as the default help format on Windows"

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

config.mak.uname

@@ -498,6 +498,7 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	NO_INET_PTON = YesPlease
 	NO_INET_NTOP = YesPlease
 	NO_POSIX_GOODIES = UnfortunatelyYes
+	DEFAULT_HELP_FORMAT = html
 	NO_D_INO_IN_DIRENT = YesPlease
 	COMPAT_CFLAGS += -D__USE_MINGW_ACCESS -DNOGDI -Icompat -Icompat/win32
 	COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"