On x64 hardware, round-trip uint64_t→double→uint64_t conversions fail for values greater than UINT64_MAX-2047. This caused the SQLite text-to-float converter routine to give incorrect results for values between '1.8446744073709550592eNNN' and '1.8446744073709551609eNNN' for any exponent NNN. Fixed by this check-in. (tags: branch-3.47)

On x64 hardware, round-trip uint64_t→double→uint64_t conversions fail for values greater than UINT64_MAX-2047. This caused the SQLite text-to-float converter routine to give incorrect results for values between '1.8446744073709550592eNNN' and '1.8446744073709551609eNNN' for any exponent NNN. Fixed by this check-in. (tags: branch-3.47)