Use .tmp before the file extension (#529)

When creating temporary files use the pattern `.tmp.ext` instead of
`.ext.tmp` to be consistent with Factorio which creates `.tmp.zip` files
during saving.

If patching fails this will leave a `.tmp.zip` file in the instance saves
directory which is ignored by the default save selector.

Resolves #486.

test/host/patch.js

@@ -15,11 +15,11 @@ describe("host/patch", function() {
 				const mappings = [
 					["locale/en/foo.cfg", "locale/en/test-foo.cfg"],
 					["locale/en/foo.txt", "locale/en/test-foo.txt"],
-					["locale/en/foo.txt.tmp", "locale/en/test-foo.txt.tmp"],
+					["locale/en/foo.tmp.txt", "locale/en/test-foo.tmp.txt"],
 					["locale/en/foo", "locale/en/test-foo"],
 					["locale/en.cfg", "locale/en/test.cfg"],
 					["locale/en.txt", "locale/en/test.txt"],
-					["locale/en.txt.tmp", "locale/en/test.txt.tmp"],
+					["locale/en.tmp.txt", "locale/en/test.tmp.txt"],
 					["locale/en", "locale/en/test"],
 					["locale/en/bar/foo.cfg", "locale/en/test-bar/foo.cfg"],
 				];

test/lib/file_ops.js

@@ -88,16 +88,30 @@ describe("lib/file_ops", function() {
 		it("should write new target file", async function() {
 			let target = path.join(baseDir, "safe", "simple.txt");
 			await lib.safeOutputFile(target, "a text file", "utf8");
-			assert(!await fs.pathExists(`${target}.tmp`), "temporary was left behind");
+			assert(!await fs.pathExists(target.replace(".txt", ".tmp.txt")), "temporary was left behind");
 			assert.equal(await fs.readFile(target, "utf8"), "a text file");
 		});
 		it("should overwrite existing target file", async function() {
 			let target = path.join(baseDir, "safe", "exists.txt");
 			await fs.outputFile(target, "previous", "utf8");
 			await lib.safeOutputFile(target, "current", "utf8");
-			assert(!await fs.pathExists(`${target}.tmp`), "temporary was left behind");
+			assert(!await fs.pathExists(target.replace(".txt", ".tmp.txt")), "temporary was left behind");
 			assert.equal(await fs.readFile(target, "utf8"), "current");
 		});
+		it("should handle creating file in current working directory", async function() {
+			let target = "temporary-file-made-to-test-cwd.txt";
+			try {
+				await lib.safeOutputFile(target, "a text file", "utf8");
+			} finally {
+				try {
+					await fs.unlink(target);
+				} catch (err) {
+					if (err.code !== "ENOENT") {
+						throw err;
+					}
+				}
+			}
+		});
 	});
 
 	describe("checkFilename()", function() {