Block alias :with_mapfile{...}:with_mapfile.

Such alias pair obsoletes functions run_code_with_mapfile:(),
load_module_mapfile(), and unload_module_mapfile() via the newfound static
block alias metaphor.

Refactored numerous calls from get_file_text() to :set_string_to_file_text().
Various other getter calls were similarly refactored, as well.

Renamed :try{...}:always{...}:always to :try{...}:catch{...}:catch. The new
nomenclature should be reasonably stable going forward, given that we're
actually somewhat partial to it. (Something never attributable to the prior
syntax, certainly.)