Fix problem with python and change of PATH

- waits that lyxrc has been read before finding python
- when the PATH changes, resets the value

src/LyXRC.cpp

@@ -2987,6 +2987,8 @@ void actOnUpdatedPrefs(LyXRC const & lyxrc_orig, LyXRC const & lyxrc_new)
 	case LyXRC::RC_PATH_PREFIX:
 		if (lyxrc_orig.path_prefix != lyxrc_new.path_prefix) {
 			prependEnvPath("PATH", lyxrc_new.path_prefix);
+			// Resets python path
+			support::os::python(true);
 		}
 	case LyXRC::RC_PREVIEW:
 	case LyXRC::RC_PREVIEW_HASHED_LABELS:

src/support/Package.cpp

@@ -159,11 +159,6 @@ Package::Package(string const & command_line_arg0,
 	explicit_user_support_dir_ = userSupportDir(default_user_support_dir,
 				     command_line_user_support_dir, user_support_dir_);
 
-	FileName const configure_script(addName(system_support().absFileName(), "configure.py"));
-	configure_command_ = os::python() + ' ' +
-			quoteName(configure_script.toFilesystemEncoding(), quote_python) +
-			with_version_suffix();
-
 	LYXERR(Debug::INIT, "<package>\n"
 		<< "\tbinary_dir " << binary_dir().absFileName() << '\n'
 		<< "\tsystem_support " << system_support().absFileName() << '\n'
@@ -176,6 +171,19 @@ Package::Package(string const & command_line_arg0,
 		<< "</package>\n");
 }
 
+std::string const & Package::configure_command() const
+{
+	if (configure_command_.empty()) {
+		std::string &command = const_cast<std::string&>(configure_command_);
+		FileName const configure_script(addName(system_support().absFileName(), "configure.py"));
+		command = os::python() + ' ' +
+			quoteName(configure_script.toFilesystemEncoding()) +
+			with_version_suffix() + " --binary-dir=" +
+			quoteName(FileName(binary_dir().absFileName()).toFilesystemEncoding());
+	}
+	return configure_command_;
+}
+
 
 void Package::set_temp_dir(FileName const & temp_dir) const
 {

src/support/Package.h

@@ -144,7 +144,7 @@ public:
 	 *  Caution: This is "ready-to-run", i.e. in the locale encoding, not
 	 *  utf8.
 	 */
-	std::string const & configure_command() const { return configure_command_; }
+	std::string const & configure_command() const;
 
 private:
 	FileName binary_dir_;

src/support/os.cpp

@@ -60,10 +60,13 @@ int timeout_min()
 }
 
 
-string const python()
+string const python(bool reset)
 {
 	// Check whether the first python in PATH is the right one.
 	static string command = python2("python -tt");
+	if (reset) {
+		command = python2("python -tt");
+	}
 
 	if (command.empty()) {
 		// It was not, so check whether we can find it elsewhere in

src/support/os.h

@@ -59,7 +59,8 @@ shell_type shell();
 int timeout_min();
 
 /// Name of the python interpreter
-std::string const python();
+/// @param reset True if the python path should be recomputed
+std::string const python(bool reset = false);
 
 ///
 bool isFilesystemCaseSensitive();