Introduced ChecksumPolicy SPI for repository connectors to consult for checksum validation

Simple refactoring transformations without logic change

Actual flow of code is somehow becoming visible. I wonder how things got this bad....

Extracted method and got rid of outer label/continue statement

Bug 419314 - Allow to determine whether artifact/metadata resolution exceptions have been played back from the error cache

Added isFromCache() property to (Artifact|Metadata)TransferException

Made PathRecordingDependencyVisitor stop traversal upon cycle entry, also added test to verify NearestVersionSelector's usage of PathRecordingDependencyVisitor does not suffer from cycle-related issues either

Made DefaultUpdateCheckManager support aether.updateCheckManager.sessionState configuration property to bypass or disable in-session state

Added JreProxySelector to aether-util

Made HttpTransporter check for WebDAV-capable server and issue MKCOL requests as needed to create missing parent directories before the actual PUT

Made DefaultInstaller bail out with exception if source and destination of install operation are equal

Wrapping a stream that is read/written in large chunks with BufferedXXStream is
useless, causing excessive copying of data and reduced performance

Wrapping a FileOutputStream that is written in chunks of 32K with an 8K BufferedOutputStram
produces only hot air and no performance gain. (Actually a perf. reduction)