SI-7261 BooleanSetting to Boolean conversion

Add an implicit for BooleanSetting to Boolean, since while we never
expect the Spanish Inquisition, we do expect a boolean in an if clause.

The first cut put the implicit at AbsScalaSettings, but the more
general case is at reflect/internal's MutableSettings.  There was no
particular desire to privilege mutability.
SI-7261 Applications of BooleanSetting to Boolean conversion

Most BooleanSettings are accessed in a conditional, but the verbiage
of settings.myflag.value gave rise frequent tmp vals.  These are
usually eliminated in favor of an import, hence if (myflag).

Convert BooleanSetting to BooleanFlag.  You'd think that would be trivial, if necessary.

There are a few minor s"$tweaks" for readability.

A few trailing case ex: that confuse vi modelines are mitigated.