cmake-gui: Change --install to use /usr/local/bin by default (#15627)

In commit v3.3.0-rc1~49^2~2 (cmake-gui: Add --install option to add
command-line tools on OS X, 2015-05-19) the option default was set to
/usr/bin because that is where the old command line install dialog
placed the symlinks.  A better default is /usr/local/bin because it is
meant for locally installed software rather than Apple-installed tools.
Also, as of OS X El Capitan, special privileges are required even for
root to modify /usr/bin but not /usr/local/bin.

Source/QtDialog/CMakeSetup.cxx

@@ -84,7 +84,7 @@ int main(int argc, char** argv)
 #if defined(Q_OS_MAC)
   if (argc2 == 2 && strcmp(argv2[1], "--install") == 0)
     {
-    return cmOSXInstall("/usr/bin");
+    return cmOSXInstall("/usr/local/bin");
     }
   if (argc2 == 2 && cmHasLiteralPrefix(argv2[1], "--install="))
     {

Source/QtDialog/CMakeSetupDialog.cxx

@@ -425,7 +425,7 @@ void CMakeSetupDialog::doInstallForCommandLine()
     "\n"
     " PATH=\"%1\":\"$PATH\"\n"
     "\n"
-    "Or, to install symlinks to '/usr/bin', run:\n"
+    "Or, to install symlinks to '/usr/local/bin', run:\n"
     "\n"
     " sudo \"%2\" --install\n"
     "\n"