Avoid forcing the user to rerun with bogus background monitor setup

[t-b]

• Run a MIES hardware test: runwithOpts(testsuite = "UTF_PatchSeqDAScale_Adapt.ipf", testcase = "PS_DS_AD1", allowdebug=1)
• Abort it while running with SHIFT+ESC

try running it again with
runwithOpts(testsuite = "UTF_PatchSeqDAScale_Adapt.ipf", testcase = "PS_DS_AD1", allowdebug=1)

this gives

  Fatal: RunTest was called by user after background monitoring was registered. This is not supported.

I do get that quite often during development. I would prefer a warning message only and then that it tries to recover by itself without me having to call it again.