Support !include wildcard-pattern

This allows auto-inclusion of sub-directories of config files (e.g. !include modopts.d/*.ini). This, along with the next commit to js_file.c, allows module authors (or sysops) to keep their module-specific settings in a module-specific file (rather than always merging-with/managing the monolithic/shared modopts.ini). The [modname] section heading is still required in the included .ini file.

Replaced use of non-thread-safe STRERROR() with safe_strerror().