fixed a crash when a token contains non-escaped backslashes, and added a unit test

src/base/detoken.lua

@@ -139,7 +139,8 @@
 				end
 				return value
 			else
-				return expandvalue(value)
+				-- escape backslashes: they will break loadstring
+				return expandvalue(value:gsub("\\", "\\\\"))
 			end
 		end
 

tests/base/test_detoken.lua

@@ -119,3 +119,13 @@
 		x = detoken.expand(os.getcwd() .. "/%{cfg.objdir}/file", environ, {paths=true,pathVars=true})
 		test.isequal("$(IntDir)/file", x)
 	end
+
+--
+-- Escapes backslashes correctly.
+--
+
+	function suite.escapesBackslashes()
+		environ.foo = "some/path"
+		x = detoken.expand("%{foo:gsub('/', '\\')}", environ)
+		test.isequal("some\\path", x)
+	end