Limit getheaders to a hard 2000.

Previously getheaders would return any number of headers up to
2000 + the distance the locator parameter was back (which is up to
~ the number of items in the locator ^ 2).

The only client I was able to find which actually handles the headers
message is BitcoinJ, and it clearly expects no more than 2000 headers
See:
http://code.google.com/p/bitcoinj/source/browse/core/src/main/java/com/google/bitcoin/core/HeadersMessage.java#35

Additionally, the wiki clearly states that getheaders will only ever
return 2000 headers: https://en.bitcoin.it/wiki/Network#Messages
Add Luke-Jr's PGP key to gitian-downloader
removed an ugly line break in a transaction tooltip for case TransactionStatus::Mature
made tray icon tooltip translatable
fixed typo in comment in netbase.h and bignum.h
Updated my GPG key
hide Delete button (only) on ReceivingTab / hide Sign message button (only) on SendingTab
Bump version to 0.6.0.99 for 0.6.1 merge window
Increase time ago of last block for "up to date" status from 30 to 90 minutes

It was too hyperactive.
gmaxwell: I mean that right now when the block gap goes over an hour it starts showing synchronizing. Increasing that to 90 minutes or so would make it only happen about 6.4 times per year
modified block DL progressbar to be dynamic and more precise
removed relative progressbar display and moved re-worked network detection code to setNumBlocks()
changed progressbar text to "~n blocks remaining"
implemented OS independent progress bar style / moved one-time functions used on the bar to a better code location
color update for progress bar
polished code and fixed progress display (was very jerky at the end of a sync)
changed percentage done in tooltip to float to be more precise / allowed plurals in translation for "x block(s) remaining"
clarified comment why we use an own progressbar style / included "~" in the tr() call
VC2010 compile fixes
move QT_PLUGINS stuff to qt main file, where it belongs
Code deduplication: make function in GUIUtil to get connection type to call object slot in GUI thread
with invokeMethod.