Addresses TTP 332274 (mainly CrashReportClientApp.cpp changes) and
- Fixes hang on Linux (uploader wasn't honoring always-unattended setting)
- Fixed erroneous check warnings
- Removed code duplication between CrashReportClient platforms
- Error message now passed on for ensures as well as asserts
- Windows crash reporting multiple instance bail-out is now thread-safe
#CodeReview Bob.Tellez, Jaroslaw.Surowiec
[CL 2077477 by James Hopkin in Main branch]