Clarify locale assumptions.
Add locale sanity check making sure the global bitcoind C and C++ locales are set to the classic "C" locale (the minimal locale).
Add locale sanity check making sure the global bitcoin-qt C++ locale is set to the classic "C" locale (the minimal locale). (We do not assume any specific C locale in bitcoin-qt.)
To summarize - assumed locales:
| Program | C locale ( setlocale) | Global C++ locale ( std::locale) | 
|---|---|---|
| bitcoind | C(classic) | C(classic) | 
| bitcoin-qt | No assumed locale | C(classic) |