Fixed an issue where some preflight failures could be ignored, changing
return code for do_preflight_checks() from 0 to "$ErrorCount".
Also, changes in behavior to undocumented '-I' flag:
If '-I' is specified, the ErrorCount is reset to zero after preflight checks,
so we don't get a FAILURE indication if the upgrade succeeded despite ignored
warnings. This also allows custom post-processing scripts to execute upon
successful completion of an upgrade with ignored warnings.
Any new errors subsequent to preflight checks will result in a FAILURE