Tighten scope of the FileInputStream in WalletAppKit to avoid lock collisions on Windows. Resolves issue 556.
Fixes to tagging, thanks to Andreas for the review.

- Wallet now forces immediate autosave when a tag is set.
- TaggableObject javadocs s/wallet/object/
BloomFilter: set a lower bound on nHashFuncs of 1: there must always be at least one function. Thanks to Kalpesh Parmar for debugging this.

Static import Math for shorter more readable code.
Fixed checkpoint builder
Merge branch 'master' of github.com:bitcoinj/bitcoinj