Bitcoin-Qt: prevent stuck/unusable debug window on exit
Bitcoin-Qt: prevent stuck/unusable debug window on exit

- when closing the client with an open debug window, that window could
  become stuck/unsuable (it was still shown wherea the main window was
  hidden already)
- fix this by hiding the debug window, when quitting the the client

Rebased-from: 3f8241c65539ceae7dc858f6f85acf3c2c58253b 0.8.x

brishtiteveja/sherlockholmescoin,Tetcoin/tetcoin,netswift/vertcoin,Ziftr/litecoin,mooncoin-project/mooncoin-landann,gwangjin2/gwangcoin-core,coinkeeper/2015-06-22_18-51_vertcoin,shapiroisme/datadollar,coinkeeper/2015-06-22_19-13_florincoin,oklink-dev/litecoin_block,koharjidan/litecoin,earthcoinproject/earthcoin,plankton12345/litecoin,gwangjin2/gwangcoin-core,IlfirinIlfirin/shavercoin,shadowoneau/ozcoin,netswift/vertcoin,wekuiz/wekoin,IlfirinIlfirin/shavercoin,mrtexaznl/mediterraneancoin,Rav3nPL/doubloons-08,Tetcoin/tetcoin,earthcoinproject/earthcoin,Litecoindark/LTCD,ohac/sha1coin,greencoin-dev/greencoin-dev,greencoin-dev/greencoin-dev,coinkeeper/2015-04-19_21-20_litecoindark,wekuiz/wekoin,stamhe/litecoin,Rav3nPL/doubloons-08,koharjidan/litecoin,mrtexaznl/mediterraneancoin,neutrinofoundation/neutrino-digital-currency,Electronic-Gulden-Foundation/egulden,IlfirinCano/shavercoin,ccoin-project/ccoin,Tetcoin/tetcoin,Czarcoin/czarcoin,earthcoinproject/earthcoin,kryptokredyt/ProjektZespolowyCoin,ohac/sha1coin,dakk/soundcoin,alexandrcoin/vertcoin,greencoin-dev/greencoin-dev,vertcoin/eyeglass,shadowoneau/ozcoin,ccoin-project/ccoin,Tetcoin/tetcoin,ohac/sha1coin,zebrains/Blotter,shapiroisme/datadollar,wekuiz/wekoin,Rav3nPL/doubloons-08,gwangjin2/gwangcoin-core,brishtiteveja/sherlockholmescoin,kryptokredyt/ProjektZespolowyCoin,dakk/soundcoin,IlfirinIlfirin/shavercoin,kryptokredyt/ProjektZespolowyCoin,zebrains/Blotter,Czarcoin/czarcoin,neutrinofoundation/neutrino-digital-currency,coinkeeper/2015-04-19_21-20_litecoindark,gwangjin2/gwangcoin-core,okinc/litecoin,Electronic-Gulden-Foundation/egulden,Ziftr/litecoin,plankton12345/litecoin,stamhe/litecoin,stamhe/litecoin,shadowoneau/ozcoin,mrtexaznl/mediterraneancoin,okinc/litecoin,okinc/litecoin,ohac/sha1coin,ccoin-project/ccoin,Czarcoin/czarcoin,Ziftr/litecoin,vertcoin/eyeglass,zebrains/Blotter,IlfirinCano/shavercoin,mrtexaznl/mediterraneancoin,novaexchange/EAC,Litecoindark/LTCD,earthcoinproject/earthcoin,shadowoneau/ozcoin,zemrys/vertcoin,Rav3nPL/doubloons-08,coinkeeper/2015-06-22_19-13_florincoin,coinkeeper/2015-06-22_19-13_florincoin,ohac/sakuracoin,alexandrcoin/vertcoin,zemrys/vertcoin,coinkeeper/2015-06-22_18-51_vertcoin,zebrains/Blotter,novaexchange/EAC,novaexchange/EAC,dakk/soundcoin,neutrinofoundation/neutrino-digital-currency,wekuiz/wekoin,zemrys/vertcoin,mooncoin-project/mooncoin-landann,mooncoin-project/mooncoin-landann,Czarcoin/czarcoin,gwangjin2/gwangcoin-core,coinkeeper/2015-06-22_18-51_vertcoin,netswift/vertcoin,Ziftr/litecoin,zemrys/vertcoin,Litecoindark/LTCD,coinkeeper/2015-06-22_19-13_florincoin,plankton12345/litecoin,oklink-dev/litecoin_block,ohac/sakuracoin,ohac/sha1coin,kryptokredyt/ProjektZespolowyCoin,novaexchange/EAC,netswift/vertcoin,netswift/vertcoin,mooncoin-project/mooncoin-landann,kryptokredyt/ProjektZespolowyCoin,coinkeeper/2015-06-22_18-51_vertcoin,coinkeeper/2015-04-19_21-20_litecoindark,novaexchange/EAC,koharjidan/litecoin,shapiroisme/datadollar,brishtiteveja/sherlockholmescoin,Litecoindark/LTCD,koharjidan/litecoin,Rav3nPL/doubloons-08,greencoin-dev/greencoin-dev,stamhe/litecoin,ohac/sakuracoin,alexandrcoin/vertcoin,zemrys/vertcoin,Tetcoin/tetcoin,Litecoindark/LTCD,coinkeeper/2015-04-19_21-20_litecoindark,plankton12345/litecoin,coinkeeper/2015-06-22_19-13_florincoin,greencoin-dev/greencoin-dev,oklink-dev/litecoin_block,ccoin-project/ccoin,IlfirinIlfirin/shavercoin,IlfirinCano/shavercoin,coinkeeper/2015-06-22_18-51_vertcoin,plankton12345/litecoin,dakk/soundcoin,IlfirinIlfirin/shavercoin,Ziftr/litecoin,brishtiteveja/sherlockholmescoin,brishtiteveja/sherlockholmescoin,IlfirinCano/shavercoin,ohac/sakuracoin,okinc/litecoin,vertcoin/eyeglass,IlfirinCano/shavercoin,Electronic-Gulden-Foundation/egulden,Electronic-Gulden-Foundation/egulden,shapiroisme/datadollar,okinc/litecoin,alexandrcoin/vertcoin,netswift/vertcoin,Electronic-Gulden-Foundation/egulden,ohac/sakuracoin,oklink-dev/litecoin_block,vertcoin/eyeglass,shapiroisme/datadollar,earthcoinproject/earthcoin,shadowoneau/ozcoin,koharjidan/litecoin,dakk/soundcoin,zemrys/vertcoin,coinkeeper/2015-04-19_21-20_litecoindark,mooncoin-project/mooncoin-landann,Czarcoin/czarcoin,koharjidan/litecoin,zebrains/Blotter,wekuiz/wekoin,neutrinofoundation/neutrino-digital-currency,Electronic-Gulden-Foundation/egulden,oklink-dev/litecoin_block,mrtexaznl/mediterraneancoin,vertcoin/eyeglass