Control module command verbosity

The ability to control message verbosity has been added so module command can be configured whether it should display more or less information. Available verbosity levels from the least to the most verbose are:

silent: turn off error, warning and informational messages but does not affect module command output result.

concise: enable error and warning messages but disable informational messages.

normal: turn on informational messages, like a report of the additional module evaluations triggered by loading or unloading modules, aborted evaluation issues or a report of each module evaluation occurring during a restore or source sub-commands.

verbose: add additional informational messages, like a systematic report of the loading or unloading module evaluations.

debug: print debugging messages about module command execution.

Default verbosity level can be controlled at configure time with the --with-verbosity option, which could be passed any of the above level names. This default verbosity level could be superseded with the MODULES_VERBOSITY environment variable, which could be set through the config sub-command with the verbosity option. Command-line switches --silent, --verbose and --debug supersede in turns any other verbosity configuration to respectively set module command silent, verbose or in debug mode.

This new feature will be included into the imminent v4.3 release.