allow txindex to be removed and add a reindex dialog

- adds a reindex dialog for Bitcoin-Qt to change -txindex without the need
  to supply -reindex
- now also does a -reindex, when removing the -txindex switch
fix comment about dust logic
send tx relay flag with version
Remove broken option to skip input checking for wallet txn.
fixed: include boost header as necessary

Without this include, sometimes BOOST_VERSION was defined and sometimes
it was not, depending on which includes came before it. The result was a
random mix of sleep or sleep_for for boost versions >= 1.50.
fixed: don't use thread::sleep_for where it's known to be broken

Fixes #2690.
Merge pull request #2769 from TheBlueMatt/master

Remove broken option to skip input checking for wallet txn.
Merge pull request #2766 from theuni/fix-shutdown-deadlock

Fix shutdown deadlock, ticket #2690
Merge pull request #2648 from Diapolo/txindex

allow txindex to be removed and add a reindex dialog
Merge pull request #2763 from bitsofproof/master

Send tx relay flag with version message
Merge pull request #2760 from cozz/cozz2

fix comment about dust logic