Drop fees by 10x due to the persistently higher exchange rate.

The last fee drop was by 5x (from 50k satoshis to 10k satoshis)
in the 0.8.2 release which was about 6 months ago.

The current fee is (assuming a $500 exchange rate) about 5 dollar
cents. The new fee after this patch is 0.5 cents.

Miners who prefer the higher fees are obviously still able to
use the command line flags to override this setting. Miners who
choose to create smaller blocks will select the highest-fee paying
transactions anyway.

This would hopefully be the last manual adjustment ever required
before floating fees become normal.
Adds additional zero checks for setCompact
 These encoded values should all decode to zero

   Positive Numbers
    0x01003456 (1 byte  0x00)
    0x02000056 (2 bytes 0x0000)
    0x03000000 (3 bytes 0x000000)
    0x04000000 (4 bytes 0x000000_00)

   Negative Numbers
    0x00923456 -(0 bytes, so zero)
    0x01803456 -(1 byte  0x00)
    0x02800056 -(2 bytes 0x0000)
    0x03800000 -(3 bytes 0x000000)
    0x04800000 -(4 bytes 0x000000_00)
Don't store or send side-chain blocks lower than last checkpoint.
Per-peer block download tracking and stalled download detection.

Keep track of which block is being requested (and to be requested) from
each peer, and limit the number of blocks in-flight per peer. In addition,
detect stalled downloads, and disconnect if they persist for too long.

This means blocks are never requested twice, and should eliminate duplicate
downloads during synchronization.
Document new `walletpassphrase` behavior in 0.9

Also add a note to the release notes.
Fixes #3672.
always show syncnode in getpeerinfo (fixes #2717)
Increase default dbcache to 100 MiB
add constants for shared (GUI/core) -dbcache settings

- adds nDefaultDbCache, nMaxDbCache and nMinDbCache in txdb.h
[Qt] small .ui cleanup for optionsdialog and coincontrol
Merge pull request #3679 from laanwj/2014_02_walletpassphrase_behavior

Document new `walletpassphrase` behavior in 0.9
Fix crash in importwallet and dumpwallet formatting

- DecodeDumpTime was passing a statically allocated facet object to
  std::locale. However, "The constructed locale object takes over
  responsibility for deleting this facet object." causing a free()
  crash on scope exit. Fixes #3670.

- EncodeDumpTime was using the wrong format character for dates
  (appears accidentally introduced in 51ed9ec9)
Merge pull request #3691

a143d4c Fix crash in importwallet and dumpwallet formatting (Wladimir J. van der Laan)
Merge pull request #3687

82e9600 add constants for shared (GUI/core) -dbcache settings (Philip Kaufmann)
879b390 Increase default dbcache to 100 MiB (Pieter Wuille)
Merge pull request #3693

f05fa03 [Qt] small .ui cleanup for optionsdialog and coincontrol (Philip Kaufmann)
Change new constants in txdb.h to int64_t

A shift overflow was happening when using these to check against in init.cpp.
Fixes #3702.
Wallet locking fixes for -DDEBUG_LOCKORDER

Compiling with -DDEBUG_LOCKORDER and running the qa/rpc-test/ regression
tests uncovered a couple of wallet methods that should (but didn't)
acquire the cs_wallet mutext.

I also changed the AssertLockHeld() routine print to stderr and
abort, instead of printing to debug.log and then assert()'ing.
It is annoying to look in debug.log to find out which
AssertLockHeld is failing.
qt: Rename 'Confirmed' balance to 'Spendable' on overview page

The word 'Spendable' more precisely says what the balance actually means.

Avoids the confirmed/unconfirmed confusion that can be caused by #3676.
Merge pull request #3699

ddcabae qt: Rename 'Confirmed' balance to 'Spendable' on overview page (Wladimir J. van der Laan)
Merge pull request #3703

ad54a9b Change new constants in txdb.h to int64_t (Wladimir J. van der Laan)
Display progress of rescan.