maint: Remove dietncl/errmsg.lua
maint: Syntax cleanup and comment fixes

* dietncl/filter/import.lua: Likewise.
* dietncl/filter/region.lua: Likewise.
* dietncl/init.lua: Likewise.
* dietncl/path.lua: Likewise.
* dietncl/xmlsugar.lua: Likewise.
* tests/test-filter-import.lua: Likewise.
* tests/test-filter-region.lua: Likewise.
* tests/test-init-parse.lua: Likewise.
* tests/test-init-parsestring.lua: Likewise.
* tests/test-path-absolute.lua: Likewise.
* tests/test-path-join.lua: Likewise.
* tests/test-path-relative.lua: Likewise.
* tests/test-path-split.lua: Likewise.
* tests/test-xmlsugar-attributes.lua: Likewise.
* tests/test-xmlsugar-children.lua: Likewise.
* tests/test-xmlsugar-clone.lua: Likewise.
* tests/test-xmlsugar-eval.lua: Likewise.
* tests/test-xmlsugar-gmatch.lua: Likewise.
* tests/test-xmlsugar-insert.lua: Likewise.
* tests/test-xmlsugar-match.lua: Likewise.
* tests/test-xmlsugar-remove.lua: Likewise.
* tests/test-xmlsugar-replace.lua: Likewise.
* tests/test-xmlsugar-userdata.lua: Likewise.
* tests/util.lua: Likewise.