Fixes #169: Security Issue in Parsing XML using NSXMLDocument

External entities are no longer parsed in appcasts: pre-10.7, we use the
"tidy" option for XML document parsing, which happens to behave this way,
and in 10.7+ we use a new explicit option for this behavior.
Fixing some new Clang warnings from Xcode 4.4
Fixes #170: An environment variable set by Sparkle
Fixes #174: Bug: sparkle:shortVersionString ignored for non-enclosure items
Fixes #175: Bug: update alert text collides with automatic download checkbox
support for encrypted disk images
Updating Danish localization courtesy Daniel Østergaard Nielsen
remove the ASW tags since we're submitting this as a pull request to andy
Fixes #44: maximumSystemVersion key
Removed methods from SUPasswordPrompt.h that didn't need to be exposed there
Redesigned password prompt UI
Removed changes to the project.pbxproj that were unrelated to the password prompt
Use NSFileManager interface for DMG unarchive only for 10.7+. On 10.6,  [NSFileManager copyItemAtPath:toPath:error:] can fail with "Argument list too long" if the app bundle contains too many files.
The switch to NSFileManager was only required for 10.7 anyway, 10.6 always worked fine.
Delegated password prompting to the update driver.

The SUDiskImageUnarchiver shouldn't know about UI, and besides,
it's important that update drivers which should not display UI (like
the automatically-installing and probing drivers) should not display
password prompts.
Removing Japanese localization of the password prompt, since I changed the design
Allow the user to try reentering his password if authentication fails.
Removed Japanese localization of password prompt from the Xcode project
Fixes #48: Adopt standard code signing in favor of DSA signing

Thanks to Mattt Thompson (@mattt) for tag-team-ing this with me.

With this change, if your app deploys only to 10.6+, then you can
dispense altogether with the DSA signatures on future updates to your
application: just make sure the "to" version satisfies the "from"
version's Apple code signing requirements. Most of you are probably
already doing that, and if you're not, you should be anyway.

Specifically, Sparkle validates the designated requirement of the "from"
version against the "to" version. By default, as of this writing, that
means that the bundle identifiers must be the same, and that the leaf
certificate of the signature is the same. So if you keep code signing
your app with the same cert, Sparkle will Just Work without any
additional DSA signature nonsense for you to deal with.

Traditional Sparkle DSA signatures will still be honored.

This support has only been extended to updates to the main app bundle.
If you're updating some other bundle, you will have to use DSA signatures
to secure your updates in the future.

***IMPORTANT: previously, Sparkle considered an update "safe" if both the
appcast and update were distributed over https. That is nowhere near as
strong a verification measure as code signing or the old-school DSA
signatures, so with this change, support for unsigned, https-distributed
updates has been removed. If you're targeting 10.6+, start code-signing
your apps if you haven't already, and everything will be fine. If you're
targeting earlier OS Xs, you'll need to start adding DSA signatures to
your appcasts. When you link this changed version of Sparkle into your
app, it will warn you on launch if you are not code signed and do not
have a DSA public key specified in your Info.plist.
Merge branch 'EncryptedDiskImages'
Making sure to initialize all Security types