check if SUBundleName is set before normalizing

[jfenton-tsc]

Inspired by #1442

When changing the name of an app, there's a couple things to do in order
to ensure auto-updates still work:

1. set SUBundle Name. This basically tells Sparkle "ey, expect an app
   of {SUBundleName}.(app|pkg) instead of the normal name."
2. set SPARKLE_NORMALIZE_INSTALLED_APPLICATION_NAME in
   commonConfig.xccconfig to reset the name of the app.

in (2), we always used the host's bundle name, instead of checking to
see if SUBundleName was set, which means normalization doesn't work as
expected during app name changes.

A problem that arises is that we will ALWAYS normalize the installed .app path to SUBundleName--even if the thing you're updating to has a different bundle name from SUBundleName.

I think that's expected behavior, if you specify SUBundleName and Normalize, but it does seem odd.

Testing I've done

made Some App Name.app update to Different App Name.app

• set SUBundleName to Different App Name
• compiled with SPARKLE_NORMALIZE_INSTALLED_APPLICATION_NAME = 1
• saw Some App Name.app become Different App Name.app when installing the update

made Some App Name.app update to a later build of Some App Name.app

• set SUBundleName to Different App Name
• compiled with SPARKLE_NORMALIZE_INSTALLED_APPLICATION_NAME = 1
• saw Some App Name.app become Different App Name.app when installing the update, even though it's really installing Some App Name

Other To-Dos?

• Do docs need to be updated, since this is a behavior change?
  • I think SPARKLE_NORMALIZE_INSTALLED_APPLICATION_NAME should be mentioned a bit more prominently--I had to do some digging to find out it was an option for the behavior I want
• Soliciting other users' feedback
  • it's possible (probably) that this behavior change will have an effect on others that are using it.

[kornelski]

This looks good. Thank you.