systemd-scm-0.rockspec: Fix formatting
src/id128.h: Add check_id128_t function that allows users to pass in strings to functions expecting an id128.

Update src/{journal,message}.c to use this new function
src/journal.c: Add *_unique functions
src/journal.lua: Use utility functions for field name matching/spliting
src/journal.lua: Add :each_unique(field) method. A lua iterator for unique field values