[Thermo] Fix segfault in deprecated newPhase factory function

The shared_ptr goes out of scope at the end of the function,
deleting the held ThermoPhase right as it's returned.

Erroneous behavior introduced in f3e840d (Cantera#1448).

src/thermo/ThermoFactory.cpp

@@ -202,7 +202,27 @@ ThermoPhase* newPhase(const string& infile, string id)
     warn_deprecated("newPhase",
         "To be removed after Cantera 3.0; superseded by\n"
         "newThermo(const string&, const string&).");
-    return newThermo(infile, id).get();
+    size_t dot = infile.find_last_of(".");
+    if (dot == npos) {
+        newThermoModel(infile);
+    }
+    string extension;
+    extension = toLowerCopy(infile.substr(dot+1));
+    string id_ = id;
+    if (id == "-") {
+        id_ = "";
+    }
+    if (extension == "cti" || extension == "xml") {
+        throw CanteraError("newPhase",
+                           "The CTI and XML formats are no longer supported.");
+    }
+
+    AnyMap root = AnyMap::fromYamlFile(infile);
+    AnyMap& phase = root["phases"].getMapWhere("name", id_);
+    string model = phase["thermo"].asString();
+    unique_ptr<ThermoPhase> t(ThermoFactory::factory()->create(model));
+    setupPhase(*t, phase, root);
+    return t.release();
 }
 
 void addDefaultElements(ThermoPhase& thermo, const vector<string>& element_names) {

test/thermo/ThermoPhase_Test.cpp

@@ -117,6 +117,17 @@ TEST_F(TestThermoMethods, setConcentrations)
     EXPECT_NEAR(thermo->moleFraction(2), -1e-8 / ctot, 1e-16);
 }
 
+TEST(ThermoConstructors, newPhase)
+{
+    suppress_deprecation_warnings();
+    // Test deprecated newPhase(infile, phasename) factory function
+    unique_ptr<ThermoPhase> gas(newPhase("h2o2.yaml", ""));
+    gas->setState_TPX(400, 2 * OneAtm, "H2:1.0, O2:1.0");
+    EXPECT_NEAR(gas->moleFraction("H2"), 0.5, 1e-8);
+    EXPECT_NEAR(gas->pressure(), 2 * OneAtm, 1e-5);
+    make_deprecation_warnings_fatal();
+}
+
 class EquilRatio_MixFrac_Test : public testing::Test
 {
 public: