fix: OutOfMemoryError from buildChargeTree.groovy

[c-dilks]

fixes #281

Moves monitor_*.hipo file handling to its own loop, which iterates over QA bins for each run.

HIPO files were not being closed, since monFile and inMdir never go out of scope; each new file and its histograms persists in memory.

Basically, instead of

def obj // global scope
run_list.each {
  obj = new ...
}

do this:

run_list.each {
  def obj = new ... // scoped for only this iteration
}

[jwgibbs]

The edit looks good to me. Good catch.