Migrate from .sln to .slnx

Author: commonsensesoftware

.gitattributes

@@ -23,6 +23,8 @@
 # intervention with every merge. To do so, just uncomment the entries below
 ###############################################################################
 #*.sln       merge=binary
+#*.slnx      merge=binary
+#*.slnf      merge=binary
 #*.csproj    merge=binary
 #*.vbproj    merge=binary
 #*.vcxproj   merge=binary